Abstract:

The present invention is directed to methods for making magnetically
modified electrodes and electrodes made according to the method. Such
electrode are useful as electrodes in batteries, such as Ni-MH batteries,
Ni--Cd batteries, Ni--Zn batteries and Ni--Fe batteries.

Claims:

1-9. (canceled)

10. In an electrochromic device comprising at least one electrode, the
improvement wherein said at least one electrode is magnetically modified.

11. The electrochromic device according to claim 10, wherein said at least
one electrode includes magnetic particles.

15. The electrochromic device according to claim 10, wherein said
electrochromic device comprises a viologen.

16. The electrochromic device according to claim 15, wherein said viologen
is methyl viologen or phenyl viologen.

Description:

[0001]This application is a divisional of U.S. patent application Ser. No.
11/130,231, filed May 17, 2005, which is a divisional of U.S. patent
application Ser. No. 10/406,002, filed Apr. 3, 2003 (now U.S. Pat. No.
6,949,179), which is a continuation in part of U.S. patent application
Ser. No. 09/876,035, filed Jun. 8, 2001 (now U.S. Pat. No. 6,514,575),
which is a divisional of U.S. patent application Ser. No. 09/047,494,
filed Mar. 25, 1998 (now U.S. Pat. No. 6,322,676), which is a
continuation of U.S. application Ser. No. 08/294,797, filed Aug. 25,
1994, now abandoned and claims the benefit of U.S. Provisional
Application No. 60/369,344, filed Apr. 3, 2002, each of which is
incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

[0003]1. Field of the Invention

[0004]This invention relates generally to methods for forming magnetically
modified electrodes and electrodes made by such methods. According to the
present invention, magnetically modified electrodes exhibit improved
properties compared to electrodes that are not magnetically modified.

[0005]2. Background of the Related Art

[0006]Bulk properties of molecules in magnetic fields are fairly well
understood. In the detailed description of preferred embodiments, it will
be shown that interfacial gradients in properly prepared composite
materials can be exploited to enhance flux in many types of
electrochemical systems such as fuel cells, batteries, membrane sensors,
filters and flux switches. First, however, the following discussion
provides a brief overview of the current understanding of magnetic
properties in composites. In particular, the discussion below summarizes
the thermodynamic, kinetic and mass transport properties of bulk magnetic
materials.

Rudimentary Magnetic Concepts

[0007]Paramagnetic molecules have unpaired electrons and are attracted
into a magnetic field; diamagnetic species, with all electrons paired,
are slightly repelled by the field. Radicals and oxygen are paramagnetic;
most organic molecules are diamagnetic; and most metal ions and
transition metal complexes are either para- or diamagnetic. How strongly
a molecule or species in a solution or fluid responds to a magnetic field
is parameterized by the molar magnetic susceptibility,
Pm(cm3/mole). For diamagnetic species, χm is between
(-1 to -500)@10-6 cm3/mole, and temperature independent. For
paramagnetic species, Pm ranges from 0 to +0.01 cm3/mole, and,
once corrected for its usually small diamagnetic component, varies
inversely with temperature (Curie's Law). While ions are monopoles and
will either move with or against an electric field, depending on the sign
of the ion, paramagnetic species are dipoles and will always be drawn
into (aligned in) a magnetic field, independent of the direction of the
magnetic vector. The dipole will experience a net magnetic force if a
field gradient exists. Because electrochemistry tends to involve single
electron transfer events, the majority of electrochemical reactions
should result in a net change in the magnetic susceptibility of species
near the electrode.

[0008]Magnetic field effects on chemical systems can be broken down into
three types: thermodynamic, kinetic and mass transport. Macroscopic,
thermodynamic effects are negligible, although local magnetic field
effects may not be. Kinetically, both reaction rates and product
distributions can be altered. Transport effects can lead to flux
enhancements of several-fold. Quantum mechanical effects are also
possible, especially on very short length scales, below 10 nm. The
following summarizes what has been done with homogeneous fields applied
to solutions and cells with external laboratory magnets.

Thermodynamics

[0009]A magnetic field applied homogeneously by placing a solution between
the poles of a laboratory magnet will have a negligible nonexponential
effect on the free energy of reaction.
ΔGm=-0.5ΔχmB2J /mole, where ΔGm
is the change of the free energy of reaction due to the magnetic field,
Δχm is the difference in magnetic susceptibility of the
products and reactants, and B is the magnetic induction in gauss. For the
conversion of a diamagnetic species into a paramagnetic species,
Δχm≦0.01 cm3/mole. In a 1T (1 Tesla=10 kGauss)
applied field, |ΔGm|≦0.05 J/mole. Even in the strongest
laboratory fields of 10T, the effect is negligible compared to typical
free energies of reaction (≦kJ/mole). These are macroscopic
arguments for systems where the magnet is placed external to the cell and
a uniform field is applied to the solution. Microscopically, it may be
possible to argue that local fields in composites are substantial, and
molecules in composites within a short distance of the source of the
magnetic field experience strong local fields. For example, for a
magnetic wire or cylinder, the magnetic field falls off over a distance,
χ, as χ-3. The field experienced by a molecule 1 nm from the
magnet is roughly 1021 times larger than the field experienced at 1
cm. This argument is crude, but qualitatively illustrates the potential
advantage of a microstructural magnetic composite. (As an example, in the
magnetic/Nafion (DuPont) composites, a larger fraction of the redox
species are probably transported through the 1.5 nm zone at the interface
between the Nafion and the magnetic particles.) These redox species must
therefore experience large magnetic fields in close proximity to the
interface.

Kinetics

[0010]Reaction rates, k, are parameterized by a pre-exponential factor, A,
and a free energy of activation, ΔG1; k=A exp
[-ΔG1/RT]. An externally applied, homogeneous magnetic field
will have little effect on ΔG1, but can alter A. Nonadiabatic
systems are susceptible to field effects. Magnetic fields alter the rate
of free radical singlet-triplet interconversions by lifting the
degeneracy of triplet states (affecting) G1); rates can be altered
by a factor of three in simple solvents. Because magnetic coupling occurs
through both electronic nuclear hyperfine interactions and spin-orbit
interactions, rates can be nonmonotonic functions of the applied field
strength. Photochemical and electrochemical luminescent rates can be
altered by applied fields. For singlet-triplet interconversions, magnetic
fields alter product distributions when they cause the rate of
interconversion to be comparable to the rate free radicals escape solvent
cages. These effects are largest in highly viscous media, such as polymer
films and micellar environments. Larger effects should be observed as the
dimensionality of the system decreases. For coordination complexes,
photochemical and homogeneous electron transfer rates are altered by
magnetic fields. Spin-orbit coupling is higher in transition metal
complexes than organic radicals because of higher nuclear charge and
partially unquenched orbital angular momentum of the d-shell electrons.
The rate of homogeneous electron transfer between
Co(NH3)63+ and Ru(NH3)62+ is below that
expected for diffusion controlled reactions; in a 7T magnetic field, the
rate is suppressed two to three-fold. It has been argued that
Δχ%m(and ΔGm) is set by the magnetic
susceptibility of the products, reactants, and activated complex, and a
highly paramagnetic activated complex accounts for the field effect. For
reversible electron transfer at electrodes in magnetic fields, no
significant effect is expected. For quasireversible electron transfer
with paramagnetic and diamagnetic species, electron transfer rates and
transfer coefficients (α) are unchanged by magnetic fields applied
parallel to electrodes. Magnetic fields applied perpendicular to
electrodes in flow cells generate potential differences, which just
superimpose on the applied electrode potentials. Potentials of 0.25V have
been reported. Reversing the applied magnetic field reverses the sign of
the potential difference. This effect does not change standard rate
constants, only the applied potential.

Mass Transport

[0011]Magnetically driven mass transport effects have been studied in
electrochemical cells placed between the poles of large magnets. Effects
vary depending on the orientation of the electrode, the relative
orientation of the magnetic field and the electrode, forced or natural
convection, and the relative concentrations of the redox species and
electrolyte. Three cases are illustrated in FIGS. 1, 2 and 3.

[0012]For a charged species moving by natural or forced convection
parallel to an electrode and perpendicular to a magnetic field which is
also parallel to the electrode, a Lorentz force is generated which moves
the charged particle toward the electrode (FIG. 1). This
magnetohydrodynamic effect is characterized by

F=q(E+v×B), (1)

where F, E, v, and B are vectors representing the Lorentz force on the
charged species, the electric field, the velocity of the moving species,
and the magnetic field, respective; g is the charge on the species. For
flow cells and vertical electrodes, flux enhancements of a few-fold and
reductions in the overpotential of a few tenths volts have been found in
the presence of the magnetic field. Also, embedded in Equation 1 is the
Hall effect; when a charged species moves through a perpendicular
magnetic field, a potential is generated. This potential superimposes on
the applied potential and causes migration in low electrolyte
concentrations.

[0013]When the electrode and magnetic field are parallel to the earth,
thermal motion leads to vortical motion at the electrode surface unless
the field (B) and the current density (j) are spatially invariant and
mutually perpendicular (see FIG. 2). This is parameterized as:

Fv=c-1[j×B]. (2)

In Equation (2) Fv is the vector of magnetic force per volume and c
is the speed of light. In general, these forces are smaller than Lorentz
forces; flux enhancements of a few-fold and potential shifts of 10 to 20
mV are observed. Flux enhancements of paramagnetic and diamagnetic
species are similar, but paramagnetic electrolytes enhance the flux of
diamagnetic Zn2+ two-fold. Vortices suppress thermal motion and eddy
diffusion.

[0014]The final configuration, shown in FIG. 3, is for the magnetic field
perpendicular to the electrode surface, and, therefore, parallel to the
electric field. Various, and sometimes inconsistent, results are reported
for several configurations: for vertical electrodes in quiescent
solution, flux enhancements of ≦1000%; for electrodes parallel to
the earth with forced convection, flux retardations of 10%; and for
electrodes parallel to the earth and no forced convection, both
enhancements and no enhancements are reported.

[0015]This summarizes the thermodynamic, kinetic, and mass transport
effects for systems where the magnetic field is applied uniformly across
a cell with an external magnet. None of these macroscopic effects predict
or address properties dependent on the magnetic susceptibility of the
redox species Quantum mechanical effects may also be important,
especially on short length scales.

Fuel Cells

[0016]Since the incomplete reduction of oxygen limits the efficiency of
H2/O2 solid polymer electrolyte fuel cells, the cathode must be
pressurized about five-fold over the anode.

[0017]Proton exchange membrane (PEM) fuel cell design is one which employs
hydrogen as an anode feed and oxygen in air as a cathode feed. These
fuels are decomposed electrically (to yield water) at electrodes
typically modified with a noble metal catalyst. The hydrogen and oxygen
are separated from each other by a proton exchange membrane (such as
Nafion) to prevent thermal decomposition of the fuels at the noble metal
catalysts.

[0018]However, the fuel cell is typically run under non-equilibrium
conditions, and, as such, is subject to kinetic limitations. These
limitations are usually associated with the reaction at the cathode.

O2+4H++4e=2H2O E°cathode=1.23V

[0019]As the reaction at the cathode becomes increasingly kinetically
limited, the cell voltage drops, and a second reaction path, the two
electron/two proton reduction of oxygen to peroxide, becomes increasingly
favored. This consumes oxygen in two electron steps with lower
thermodynamic potential.

O2+2H++2e=H2O2 E°H2O2=0.68V

[0020]The standard free energy of this reaction is 30% of the free energy
available from the four electron reduction of oxygen to water. The
decrease in current associated with the decreased number of electrons
transferred and the decreased cell potential couple to yield
substantially lower fuel cell power output.

[0021]One approach to enhance the efficiency of the cathodic reaction is
to increase the concentration (pressure) of the feeds to the
cathode--protons and oxygen--so as to enhance the flux (i.e., the
reaction rate at the cathode in moles/cm2s) at the cathode. The
proton flux is readily maintained at a sufficiently high value by the
proton exchange membrane (usually Nafion) so as to meet the demand set by
the cathode reaction. Normally, the method of enhancing the flux and
biasing the reaction to favor the formation of water is to pressurize the
air feed to the cathode. Pressures of 5-10 atmospheres are typical.

[0022]The need to pressurize air to the cathode in PEM fuel cells has been
a major obstacle in the development of a cost effective fuel cell as a
replacement for the internal combustion engine vehicle. In particular,
pressurization of the cathode requires compressors. In transportation
applications, power from the fuel cell is needed to run the compressor.
This results in approximately 15% reduction in the power output of the
total fuel cell system.

Free Radical Electrochemistry

[0023]Magnetic fields have been shown to affect heterogeneous and
homogeneous electron transfer reactions in aqueous matrices. In this
Chapter, we investigate magnetic effects on heterogeneous and homogeneous
free radical electron transfer mechanisms in organic matrices
(acetonitrile and methylene chloride). The systems investigated are all
systems with diamagnetic organic reactants that undergo electron transfer
reactions to form a free radical intermediate during the reaction.
Because free radicals are highly reactive with multiple reaction
pathways, we have not separated the homogeneous and heterogeneous
electron transfer effects.

[0024]All organic free radicals have EPR g-values in the range of 1.9-2.1,
values which differ substantially from the values for metal complex redox
couples. Though the EPR g-values are similar for organic radicals, the
hyperfine coupling constants can be quite different.

[0025]Magnetic effects of this sort has been investigated at a chemically
modified electrode surface. The surface of a glassy carbon electrode is
chemically modified with a composite of an ion exchange polymer and
paramagnetic microspheres. Studies at these electrodes have shown that
depending on the reactant, magnetic fields can increase, decrease, or
have no impact on flux. In some cases morphology of the voltammogram is
changed. This study shows a trend in the magnetic effects on free
radicals as a function of the relative localization of spin and charge
density in the molecule.

[0026]It has previously been determined that knowledge of spin density is
an important part of understanding magnetic properties of and effects on
paramagnetic molecules and materials. Spin and charge density are aspects
of the overall spin polarization process.

[0027]Spin density is commonly thought of in the context of magnetic
resonance spectroscopy as it relates to hyperfine coupling. Spin density
provides clues as to the intrinsic magnetic properties of a molecule.
Spin density is the probability of finding the unpaired spin localized at
a particular nuclei (N). Therefore, spin density calculations provide the
spin density at each atom in the free radical.

[0028]The unpaired spin density for a particular orbital with quantum
number n and l can be expressed as shown in equation 3.

ρ(rN)=ρH|Ψnl(rN)|2 (3)

where rN is the distance from the nucleus, p is the unpaired spin
density at the distance rN from the nucleus, Ψnl is the
wave function of the nl orbital, and ρH is the spin density in a
particular orbital. This orbital spin density is a fractional population
of unpaired electrons on an atom.

[0029]Overall spin density may be represented according to equation 4.

ρ ( r N ) = ∫ Ψ * k 2 S zk
δ ( r k - r N ) Ψ T ( 4 )
##EQU00002##

where Szk is the spin in the z direction at distance k from the
nuclei. The algebraic sum of the spin densities of each nuclei must equal
the total spin of the molecule. For the free radical systems, the total
spin is 1.0.

[0030]Hyperfine coupling constants are a function of the spin density at a
given nuclei (N), as shown in equation 5.

a = 4 π 3 g β g N β N
ρ ( r N ) ( 5 ) ##EQU00003##

The hyperfine coupling constant (a) is for a single nucleus. Total
hyperfine coupling for the entire molecule is expressed in terms of the
spin polarization constant (Q). Q is determined from the hyperfine
coupling constants (a) and the spin density constants (p(rN)) using
the according to equation 6:

Q = a H ρ ( r N ) ( 6 ) ##EQU00004##

where aH is the hyperfine coupling constant for hydrogen (H), which
is attached to heavy metal nucleus (N), and p(rN) is the spin
density of the heavy metal atom (N). Heavy metal nucleus (N) is commonly
a carbon, oxygen, nitrogen, or sulfur for these systems.

[0031]Charge has a measurable effect on Q. For instance, anthracene has
both an anion and a cation radical form. Q for the radical anion is 25
Gauss, but Q for the radical cation is 29 Gauss. The only difference
between the cation and anion radical is the charge. In order to determine
the charge localized at each nuclei (N), charge density calculations are
performed.

[0032]The above references are incorporated by reference herein where
appropriate for appropriate teachings of additional or alternative
details, features and/or technical background.

SUMMARY OF THE INVENTION

[0033]An object of the invention is to solve at least the above problems
and/or disadvantages and to provide at least the advantages described
hereinafter.

[0034]It is therefore an object of the invention to provide an improved
electrode.

[0035]Another object of the invention is to provide a coating on an
electrode to enhance the flux of magnetic species to the electrode.

[0036]Another object of the invention is to provide a separator to
separate magnetic species from each other dependent upon magnetic
susceptibility.

[0037]Another object of the invention is to provide a method for making a
coating for an electrode to improve the flux of magnetic species to the
electrode.

[0038]Another object of the invention is to provide an improved fuel cell.

[0039]Another object of the invention is to provide an improved cathode in
a fuel cell.

[0040]Another object of the invention is to provide an improved battery.

[0041]Another object of the invention is to provide an improved membrane
sensor.

[0042]Another object of the invention is to provide an improved flux
switch.

[0043]Another object of the invention is to provide an improved fuel cell
cathode with passive oxygen pressurization.

[0044]Another object of the invention is to provide an improved separator
for separating paramagnetic species from diamagnetic species.

[0045]Another object of the invention is to provide an improved
electrolytic cell.

[0046]Another object of the invention is to provide an improved
electrolytic cell for an electrolyzable gas.

[0047]Another object of the invention is to provide an improved graded
density composite for controlling chemical species transport.

[0048]Another object of the invention is to provide an improved dual
sensor.

[0049]One advantage of the invention is that it can enhance the flux of
paramagnetic species to an electrode.

[0050]Another advantage of the invention is that it can enhance the flux
of oxygen to the cathode in a fuel cell, equivalent to passive
pressurization.

[0051]Another advantage of the invention is that it can separate
paramagnetic, diamagnetic, and nonmagnetic chemical species from a
mixture.

[0052]Another advantage of the invention is that it can separate chemical
species according to chemical, viscosity, and magnetic properties.

[0053]Another advantage of the invention is that it can take advantage of
magnetic field gradients in magnetic composites.

[0054]Another advantage of the invention is that it can be designed to
work with internal or external magnetic fields, or both.

[0055]One feature of the invention is that it includes a magnetically
modified electrode.

[0056]Another feature of the invention is that it includes magnetic
composites made from ion exchange polymers and non-permanent magnet
microbeads with magnetic properties which are susceptible to externally
applied magnetic fields.

[0057]Another feature of the invention is that it includes magnetic
composites made from ion exchange polymers and organo-Fe
(superparamagnetic or ferrofluid) or other permanent magnetic and
nonpermanent magnetic or ferromagnetic or ferrimagnetic material
microbeads which exhibit magnetic field gradients.

[0058]Another object of the present invention is to provide methods for
making modified electrodes.

[0059]Another feature of the present invention is to provide magnetically
modified electrodes and articles, such as batteries, including
magnetically modified electrodes made according to the methods of the
present invention. Such batteries include primary and secondary
batteries. Examples of such batteries include, but are not limited to,
nickel-metal hydride (Ni-MH) batteries, Ni--Cd batteries, Ni--Zn
batteries and Ni--Fe batteries.

[0060]These and other objects, advantages and features are accomplished by
a separator arranged between a first region containing a first type of
particle and a second type of particle and a second region, comprising: a
first material having a first magnetism; a second material having a
second magnetism; a plurality of boundaries providing a path between the
first region and the second region, each of the plurality of boundaries
having a magnetic gradient within the path, the path having an average
width of approximately one nanometer to approximately several
micrometers, wherein the first type of particles have a first magnetic
susceptibility and the second type of particles have a second magnetic
susceptibility, wherein the first and the second magnetic
susceptibilities are sufficiently different that the first type of
particles pass into the second region while most of the second type of
particles remain in the first region.

[0061]These and other objects, advantages and features are also
accomplished by the provision of a cell, comprising: an electrolyte
including a first type of particles; a first electrode arranged in the
electrolyte; and a second electrode arranged in the electrolyte wherein
the first type of particles transform into a second type of particles
once the first type of particles reach the second electrode, the second
electrode having a surface with a coating which includes :a first
material having a first magnetism; a second material having a second
magnetism; a plurality of boundaries providing a path between the
electrolyte and the surface of the second electrode, each of the
plurality of boundaries having a magnetic gradient within the path, the
path having an average width of approximately one nanometer to
approximately several micrometers, wherein the first type of particles
have a first magnetic susceptibility and the second type of particles
have a second magnetic susceptibility, and the first and the second
magnetic susceptibilities are different.

[0062]These and other objects, advantages and features are also
accomplished by the provision of a method of making an electrode with a
surface coated with a magnetic composite with a plurality of boundary
regions with magnetic gradients having paths to the surface of the
electrode, comprising the steps of mixing a first solution which includes
a suspension of at least approximately 1 percent by weight of inert
polymer coated magnetic microbeads containing between approximately 10
percent and approximately 90 percent magnetizable polymer material having
diameters at least 0.5 micrometers in a first solvent with a second
solution of at least approximately 2 percent by weight of ion exchange
polymers in a second solvent to yield a mixed suspension; applying the
mixed suspension to the surface of the electrode, the electrode being
arranged in a magnetic field of at least approximately 0.05 Tesla and
being oriented approximately 90 degrees with respect to the normal of the
electrode surface; and evaporating the first solvent and the second
solvent to yield the electrode with a surface coated with the magnetic
composite having a plurality of boundary regions with magnetic gradients
having paths to the surface of the electrode.

[0063]These and other objects, advantages and features are further
accomplished by a method of making an electrode with a surface coated
with a composite with a plurality of boundary regions with magnetic
gradients having paths to the surface of the electrode when an external
magnetic field is turned on, comprising the steps of: mixing a first
solution which includes a suspension of at least 5 percent by weight of
inert polymer coated microbeads containing between 10 percent and 90
percent magnetizable non-permanent magnet material having diameters at
least 0.5 micrometers in a first solvent with a second solution of at
least 5 percent of ion exchange polymers in a second solvent to yield a
mixed suspension; applying the mixed suspension to the surface of the
electrode; evaporating the first solvent and the second solvent to yield
the electrode with a surface coated with the composite having a plurality
of boundary regions with magnetic gradients having paths to the surface
of the electrode when an external magnet is turned on.

[0064]These and other objects, advantages and features are also
accomplished by an electrode for channeling flux of magnetic species
comprising: a conductor; a composite of a first material having a first
magnetism and a second material having a second magnetism in surface
contact with the conductor, wherein the composite comprises a plurality
of boundaries providing pathways between the first material and the
second material, wherein the pathways channel the flux of the magnetic
species through the pathways to the conductor.

[0065]These and other objects, advantages and features are further
accomplished by an electrode for effecting electrolysis of magnetic
species comprising: a conductor; and magnetic means in surface contact
with the conductor for enhancing the flux of the magnetic species in an
electrolyte solution to the conductor and thereby effecting electrolysis
of the magnetic species.

[0066]These and other objects, advantages and features are further
accomplished by an electrode for effecting electrolysis of magnetic
species comprising: a conductor; and means in surface contact with the
conductor for enhancing the flux of the magnetic species to the conductor
and thereby effecting electrolysis of the magnetic species.

[0067]These and other objects, advantages and features are yet further
accomplished by an electrode for electrolysis of magnetic species
comprising: a conductor; a composite magnetic material in surface contact
with the conductor, the composite magnetic material having a plurality of
transport pathways through the composite magnetic material to enhance the
passage of the magnetic species to the conductor and thereby effecting
electrolysis of the magnetic species.

[0068]These and other objects, advantages and features are also
accomplished by a system, comprising: a first electrolyte species with a
first magnetic susceptibility; a second electrolyte species with a second
magnetic susceptibility; and a means for channeling the first electrolyte
species with a first magnetic susceptibility preferentially over the
second electrolyte species with a second magnetic susceptibility, wherein
the means comprises a first material having a first magnetism forming a
composite with a second material having a second magnetism.

[0069]These and other objects, advantages and features are also
accomplished by a system for separating first particles and second
particles with different magnetic susceptibilities comprising: a first
magnetic material with a first magnetism; and a second magnetic material
with a second magnetism working in conjunction with the first magnetic
material to produce magnetic gradients, wherein the magnetic gradients
separate the first particles from the second particles.

[0070]These and other objects, advantages and features are accomplished by
a composite material for controlling chemical species transport
comprising: an ion exchanger; a graded density layer, wherein the ion
exchanger is sorbed into the graded density layer.

[0071]These and other objects, advantages and features are further
accomplished by a magnetic composite material for controlling magnetic
chemical species transport according to magnetic susceptibility
comprising: an ion exchanger; a polymer coated magnetic microbead
material; and a graded density layer, wherein the ion exchanger and the
polymer coated magnetic microbead material are sorbed into the graded
density layer.

[0072]These and other objects, advantages and features are further
accomplished by a composite material for controlling chemical species
viscous transport comprising: an ion exchanger; a graded viscosity layer,
wherein the ion exchanger is sorbed into the graded viscosity layer.

[0073]These and other objects, advantages and features are further
accomplished by a magnetic composite material for controlling magnetic
chemical species transport and distribution comprising: an ion exchanger;
a polymer coated magnetic microbead material; and a graded density layer,
wherein the ion exchanger and the polymer coated magnetic microbead
material are sorbed into the graded density layer forming a gradient in
the density of the polymer coated magnetic microbead material
substantially perpendicular to a density gradient in the graded density
layer.

[0074]These and other objects, advantages and features are further
accomplished by a magnetic composite material for controlling magnetic
chemical species transport and distribution comprising: an ion exchanger;
a polymer coated magnetic microbead material; and a graded density layer,
wherein the ion exchanger and the polymer coated magnetic microbead
material are sorbed into the graded density layer forming a gradient in
the density of the polymer coated magnetic microbead material
substantially parallel to a density gradient in the graded density layer.

[0075]These and other objects, advantages and features are also
accomplished by an ion exchange composite with graded transport and
chemical properties controlling chemical species transport comprising: an
ion exchanger; and a staircase-like graded density layer having a first
side and a second side, wherein the ion exchanger is one of sorbed into
the graded density layer and cocast on the graded density layer and the
staircase-like graded density layer and the ion exchanger are contained
within the first side and the second side, wherein the first side is in
closer proximity to the source of the chemical species and the second
side is more distal to the source of the chemical species, and wherein
the staircase-like graded density layer has lower density toward the
first side and higher density toward the second side, substantially
increasing in density in a direction from the first side toward the
second side.

[0076]These and other objects, advantages and features are also
accomplished by an ion exchange composite with graded transport and
chemical properties controlling chemical species transport comprising: an
ion exchanger; and a staircase-like graded density layer having a first
side and a second side, wherein the ion exchanger is one of sorbed into
the graded density layer and cocast on the graded density layer, and the
ion exchanger and the stair case-like graded density layer are contained
within the first side and the second side, wherein the first side is in
closer proximity to the source of the chemical species and the second
side is more distal to the source of the chemical species, and wherein
the staircase-like graded density layer has higher density toward the
first side and lower density toward the second side, substantially
decreasing in density in a direction from the first side toward the
second side.

[0077]These and other objects, advantages and features are accomplished
also by a dual sensor for distinguishing between a paramagnetic species
and a diamagnetic species comprising: a magnetically modified membrane
sensor; and an unmodified membrane sensor, wherein the magnetically
modified membrane sensor preferentially enhances the concentration of and
allows the detection of the paramagnetic species over the diamagnetic
species and the unmodified membrane sensor enhances the concentration of
and allows the detection of the diamagnetic species and the paramagnetic
species, enabling the measurement of the concentration of at least the
paramagnetic species.

[0078]These and other objects, advantages and features are further
accomplished by a dual sensor for distinguishing between a paramagnetic
species and a nonmagnetic species comprising: a magnetically modified
membrane sensor; an unmodified membrane sensor, wherein the magnetically
modified membrane sensor preferentially enhances the concentration of and
allows the detection of the paramagnetic species over the nonmagnetic
species and the unmodified membrane sensor enhances the concentration of
and allows the detection of the nonmagnetic species and the paramagnetic
species, enabling the measurement of the concentration of at least the
paramagnetic species.

[0079]These and other objects, advantages and features are further
accomplished by a dual sensor for distinguishing between a first
diamagnetic species and a second diamagnetic species comprising: a
magnetically modified membrane sensor; and a differently magnetically
modified membrane sensor; wherein the magnetically modified membrane
sensor preferentially enhances the concentration of and allows the
detection of the first diamagnetic species over the second diamagnetic
species and the differently magnetically modified membrane sensor
enhances the concentration of and allows the detection of the second
paramagnetic species and the diamagnetic species, enabling the
measurement of the concentration of at least the first diamagnetic
species.

[0080]These and other objects, advantages and features are further
accomplished by a dual sensor for distinguishing between a first
paramagnetic species and a second paramagnetic species comprising: a
magnetically modified membrane sensor; and a differently magnetically
modified membrane sensor, wherein the magnetically modified membrane
sensor preferentially enhances the concentration of and allows the
detection of the first paramagnetic species over the second paramagnetic
species and the differently magnetically modified membrane sensor
enhances the concentration of and allows the detection of the second
paramagnetic species and the first paramagnetic species, enabling the
measurement of the concentration of at least the first paramagnetic
species.

[0081]These and other objects, advantages and features are further
accomplished by a dual sensor for distinguishing between a diamagnetic
species and a nonmagnetic species comprising: a magnetically modified
membrane sensor; and an unmodified membrane sensor, wherein the
magnetically modified membrane sensor preferentially enhances the
concentration of and allows the detection of the diamagnetic species over
the nonmagnetic species and the unmodified membrane sensor enhances the
concentration of and allows the detection of the nonmagnetic species and
the diamagnetic species, enabling the measurement of the concentration of
at least the diamagnetic species.

[0082]These and other objects, advantages and features are further
accomplished by a flux switch to regulate the flow of a redox species
comprising: an electrode; a coating on the electrode, wherein the coating
is formed from a composite comprising: a magnetic microbead material with
aligned surface magnetic field; an ion exchange polymer; and an
electro-active polymer in which a first redox form is paramagnetic and a
second redox form is diamagnetic, wherein the flux switch is actuated by
electrolyzing the electro-active polymer from the first redox form
ordered in the magnetic field established by the coating to the second
redox form disordered in the magnetic field.

[0083]These and other objects, advantages and features are also
accomplished by a flux switch to regulate the flow of a chemical species
comprising: an electrode; and a coating on the electrode, wherein the
coating is formed from a composite comprising: a non-permanent magnetic
microbead material; an ion exchange polymer; and a polymer with magnetic
material contained therein in which a first form is paramagnetic and a
second form is diamagnetic, wherein the flux switch is actuated by
reversibly converting from the paramagnetic form to the diamagnetic form
when an externally applied magnetic field is turned on and off.

[0084]These and other objects, advantages and features of the present
invention are accomplished by a method for forming a magnetically
modified electrode, which comprises: providing a substrate comprising a
magnetic material; and forming a coating layer on said substrate, wherein
said coating layer comprises particles capable of generating
electrochemical energy in the presence of a magnetic field.

[0085]These and other objects, advantages and features of the present
invention are accomplished by a method for forming a magnetically
modified electrode, which comprises: providing a substrate; and forming a
coating layer on said substrate, wherein said coating layer comprises
particles capable of generating electrochemical energy in the presence of
a magnetic field and magnetic particles.

[0086]These and other objects, advantages and features of the present
invention are accomplished by a method for forming a magnetically
modified electrode, which comprises: providing a substrate; and forming a
coating layer comprising particles capable of generating electrochemical
energy in the presence of a magnetic field on said substrate, wherein
said method further comprises subjecting said particles to an external
magnetic field before, during or after forming said coating layer.

[0087]These and other objects, advantages and features of the present
invention are accomplished a magnetically modified electrode, which
comprises: a substrate and a coating layer formed on said substrate,
wherein said coating layer comprises particles capable of generating
electrochemical energy in the presence of a magnetic field and magnetic
particles.

[0088]These and other objects, advantages and features of the present
invention are accomplished a magnetically modified electrode, which
comprises: a magnetic substrate and a coating layer formed on said
substrate, wherein said coating layer comprises particles capable of
generating electrochemical energy in the presence of a magnetic field.

[0089]These and other objects, advantages and features of the present
invention are accomplished a magnetically modified electrode, which
comprises: a substrate and a coating layer formed on said substrate,
wherein said coating layer comprises particles capable of generating
electrochemical energy in the presence of a magnetic field and further
wherein said particles capable of generating electrochemical energy in
the presence of a magnetic field are subjected to an external magnetic
field before, during or after said coating layer is formed on said
substrate.

[0090]The above and other objects, advantages and features of the
invention will become more apparent from the following description
thereof taken in conjunction with the accompanying drawings.

[0091]Additional advantages, objects, and features of the invention will
be set forth in part in the description which follows and in part will
become apparent to those having ordinary skill in the art upon
examination of the following or may be learned from practice of the
invention. The objects and advantages of the invention may be realized
and attained as particularly pointed out in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0092]The invention will be described in detail with reference to the
following drawings in which like reference numerals refer to like
elements wherein:

[0093]FIG. 1 shows the influence of electrode orientation and solvent
motion on magnetohydrodynamic fluid motion for one geometry.

[0094]FIG. 2 shows the influence of electrode orientation and solvent
motion on magnetohydrodynamic fluid motion for a second geometry.

[0095]FIG. 3 shows the influence of electrode orientation and solvent
motion on magnetohydrodynamic fluid motion for a third geometry.

[0102]FIG. 10 shows 6m values for Ru(NH3)63+ as a function of volume
fraction of microbeads in magnetic and nonmagnetic composites.

[0103]FIG. 11 shows the relative flux of redox species on the y-axis,
where the maximum cyclic voltammetric current for a composite with
magnetic microbeads is normalized by the maximum cyclic voltammetric
current for a Nafion film containing no magnetic material, with the ratio
giving the flux enhancement.

[0104]FIGS. 12A, 12B, and 12C show cyclic voltammetric results for the
reversible species Ru(NH3)63+ and Ru(bpy)32+ and for the
quasireversible species hydroquinone.

[0105]FIG. 13 shows a plot of the flux for seven redox species that is
used for predicting a roughly five-fold flux enhancement of oxygen
through a 15% magnetic Nafion composite over Nafion.

[0106]FIG. 14 shows a plot of the flux of Ru(NH3)63+ in magnetic
bead/Nafion composites increasing as the fraction of magnetic beads
increases.

[0108]FIG. 15B shows a simplified representation of embodiments of the
invention placed in an externally applied magnetic field provided by an
electromagnet to alter the magnetic properties of those embodiments,
where the field may be turned on or off, or it may be oscillated.

[0109]FIG. 16 shows a simplified diagram of a separator with no electrode
or conductive substrate which separates a mixture of particles between a
first solution and a second solution.

[0110]FIG. 17 is a short summary of steps involved in a method of making
an electrode according to two embodiments of the invention.

[0111]FIGS. 18A and 18B show a flux switch 800 to regulate the flow of a
redox species according to yet another embodiment of the invention.

[0112]FIG. 19 shows a dual sensor 900 for distinguishing between a first
species (particles A) and a second species (particles B).

[0113]FIG. 20 shows a cell 201 according to another embodiment of the
invention.

[0114]FIG. 21 shows methyl viologen dication, an organic molecule that is
commonly used in spectroelectrochemistry.

[0115]FIG. 22 shows a typical cyclic voltammogram of methyl viologen at a
Nafion modified electrode and at a 10% by wt. magnetic microsphere/Nafion
composite modified electrode.

[0151]It has been found that interfacial gradients of concentration,
charge, dielectric constant, and potential tend to establish strong,
interfacial forces which decay over a microstructural distance (1 to 100
nm). (For example, for an applied potential of 10 mV to 100 mV past the
potential of zero charge at an electrode in 0.1 M aqueous electrolyte,
the interfacial potential gradient (I electric fields) is 105 V/cm
to 106 V/cm, but it decays over a distance of about 1 nm.) In a
homogeneous matrix, with few interfaces, interfacial gradients have a
negligible effect on bulk material properties. However, in a
microstructured matrix where the ratio of surface area to volume is high,
interfacial gradients can have a large effect on, or even dictate the
properties of a composite. Models appropriate to the description of bulk
materials have been found to be unsatisfactory when applied to these
composites. Moreover, such composites provide an opportunity to design
matrices to perform functions and exhibit properties not found in
homogeneous materials as will be discussed.

[0152]The effects of gradients, associated with the interfaces between the
ion exchanger and its support matrix, to enhance the transport of ions
and molecules have been studied in ion exchange polymer composites. The
composites were formed by sorbing ion exchange polymers into high surface
area substrates with well-established geometries. The flux of solutes
through the composites was determined voltammetrically. When the solute
flux through the ion exchange portion of the composites and the flux
through simple films of the ion exchanger were compared, flux
enhancements were observed. These enhancements were often greater than an
order of magnitude. Consistently, the ratio of surface area of the
substrate to the volume of sorbed ion exchanger (SA/Vol) has been the
critical factor in quantifying the flux enhancements. The flux
enhancement characteristics were found to be dominated by the interface
between the ion exchanger and the support. Several interfacial gradients
have so far been identified as important: concentration gradients,
leading to surface diffusion; electric potential gradients, leading to
migration; and magnetic field gradients, leading to flux enhancements and
electric potential shifts at electrodes.

Forming Composites

[0153]Composites were made by intimately mixing two or more components to
form a heterogeneous matrix as will be discussed in more detail below.
While composites retain some characteristics of their components,
properties distinct from those of the starting materials have been
demonstrated that make composites of special interest.

Results

[0154]The impact of microstructure on transport and selectivity in ion
exchange polymers and their composites has been found to be significant.
Novel characteristics arose not from the individual components of the
composites, but from gradients established at the interfaces between the
components. Ion exchange polymers with inherent microstructure, such as
Nafion, exhibit superior transport, selectivity, and stability
characteristics compared to polymers with no inherent microstructure,
such as poly(styrene sulfonate). When ion exchange polymers were
supported on inert substrates with microstructural (5 to 100 nm) features
similar in length scale to the microstructural features of the ion
exchanger (e.g., 5 nm micelles in Nafion), the structure of the ion
exchanger was disrupted in an ordered manner. The relationship between
the flux characteristics of the composites and the microstructure imposed
by the substrates has yielded information about how microstructure
contributes to the properties of ion exchangers. This relationship allows
the specification of design paradigms for tailoring composites with
specific transport and selectivity characteristics.

Surface Diffusion

[0155]The first composites studied were formed by sorbing Nafion into the
collinear cylindrical pores of neutron track etched polycarbonate
membranes. The ion exchange polymer, Nafion is a perfluorinated, sulfonic
acid polymer with the following structure:

##STR00001##

[0156]The SO3.sup.- groups adsorb on the inert substrates to form a
loosely packed monolayer of perfluorinated alkyl chains,
OCF2CF2OCF3CF2SO3.sup.-, shown above in
boldface. This creates a unique interfacial zone approximately 1 to 2 nm
thick along the edge formed between the ion exchange polymer and the
inert substrate. In systems with high ratio of surface area to volume, a
large fraction of the molecules and ions which passed through these
composites actually moved through this interfacial zone. That is, it was
found that the molecules and ions have higher flux in this thin
interfacial zone, where the interfacial fields were strongest.

[0157]In a given membrane, all pores had approximately the same diameter,
d, ranging between 15 and 600 nm. The flux of electro-active species
through the composites was determined by rotating disk voltammetry. In
rotating disk voltammetry, the product 6m (cm2/s) parameterizes the
flux of a redox species through the Nafion portion of the composites,
where 6 is the partition coefficient of the species into the Nafion and m
(cm2/s) is its mass transport coefficient. Simple Nafion films cast
directly onto the electrode were also studied. The resulting plots of 6m
as a function of log(d) are shown in FIG. 4A. As indicated in FIG. 4A, as
the pore diameter decreased towards 30 nm, the flux through the Nafion
portion increased as much as 3600% over the simple films. These studies
showed that the interface between Nafion and a support matrix was pivotal
in determining the flux characteristics of the composites.

[0158]The flux enhancement model proposed here depends on the interface
formed between the Nafion and the polycarbonate providing facile
transport pathway to the electrode for the redox species. Bulk Nafion
located in the center of the pore had a smaller transport coefficient (m)
than the support matrix wall, but provided a volume to extract redox
species from the center of the pore to feed the wall transport zone. The
critical parameter for flux enhancement was found to be (for a
cylindrical cross section path) the ratio of the surface area of the wall
providing facile transport (πdλ), where 8 is the layer
thickness, to the volume of Nafion feeding the interface
(πdeλ/4), i.e., 4/d. Plots of 6m versus 1/d are shown in
FIG. 4B. Note that the plots are linear in FIG. 4B for d≧30 nm,
and with the exception of dopamine, the intercepts as
d→∞(1/d→0) correspond to 6m for bulk Nafion.

[0159]Predictive models of how interfaces and their associated
concentration, field, etc. gradients dictate interface properties and
function are provided below and further aid in the design of new
composites tailored for specific applications. A simple surface diffusion
model assuming no limitations to the transport rate in the radial
direction is outlined. FIGS. 5A and 5B show the simple model where
transport in the radial direction is not rate limiting. In the model
Jcomp is the total flux through the composites, JNuc is the
flux through an empty pore, and Jbulk and Jwall are the fluxes
in the bulk (center) of the pore and along the surface of the pore,
respectively. To analyze the flux, as in FIG. 4B, Jbulk and
Jwall must be normalized to the cross sectional area of the pore
used to determine 6m, the product of the effective extraction and
transport coefficients. From the final equation, the plot in FIG. 4B can
be interpreted to have the slope and intercept shown in FIGS. 5A and 5B.
If δ, the thickness of the interfacial zone, is taken as 1.5 rim,
the values cited for 6wallmwall and 6bulkmbulk are
found. The diffusion coefficients of each species in solution are also
listed for comparison. In general, 6wallmwall (10 to
102)@6bulkmbulk (1 to 10)@Dsoln. In other words, for
an interfacial zone thickness, δ, of 1.5 nm, 6wallmwall
is up to one order of magnitude higher than Dsoln, and one to two
orders of magnitude higher than 6bulkmbulk.

[0160]The interfacial transport zone occurs because of the irreversible
exchange of Nafion sulfonic acid groups to polycarbonate surface sites to
form a monolayer of inactive sulfonic acid groups. The side chains
linking the sulfonic acid sites to the Nafion backbone form a loosely
packed monolayer along the pore wall which facilitates the flux through
the transport zone compared to transport through the tortuous environment
of bulk Nafion. Given the length of the chains, a δ value of about
1.5 nm is consistent with 6wallmwall (and 6m/Dsoln)
decreasing as transport is more hindered with increasing diameter of the
redox species; i.e., 6wallmwall decreases as H2Q (0.6
nm)>Ru(NH3)63+ (0.8 nm)>DOP+ (0.8
nm6)>FerN+ (1 nm). Discrimination between these species has
also been observed based on molecular shape in the neutron track-etched
composites. For example, disk shaped molecules exhibit higher flux than
comparably sized spherical molecules.

Radial Migration

[0161]The pore walls have a surface charge density of -0.2 μC/cm2.
For a 30 nm pore diameter composite, the corresponding charge is 0.5% of
the total charge in the pore, and will have negligible effect on the
number of cations extracted from the solution to move into the pore.
However, the surface charge establishes a potential gradient (electric
field) from the pore to the wall which tends to move positively charged
ions radially outward from the center of the pore to the wall. An issue
is whether this radial, interfacial potential gradient can be coupled to
the concentration gradient along the wall to enhance solute flux to the
electrode, as illustrated in FIGS. 6A and 6B.

[0162]The model was tested by varying the concentration of the
electrolyte, nitric acid, from 0.50 to 0.01 M, for fixed dopamine
concentration (2 mM). Flux was determined by rotating disk voltammetry at
400 rpm for the bare electrode and at infinite rotation rate for the
modified electrodes (See Table 1). The electrolyte concentration did not
dramatically affect the flux for the bare electrode, the 30 nm membrane
containing no Nafion, and the Nafion

However, for the 30 nm Nafion composite a fifty-fold decrease in
electrolyte concentration led to >1600% increase in flux. Coupling of
radial flux, driven by the interfacial potential gradient, to surface
diffusion generates the enhancement. No enhancements were observed for a
similar study of neutral hydroquinone. It should be noted that only
charged species move by migration; dopamine is charged, while
hydroquinone is not.

[0163]Since the selectivity coefficient for dopamine over protons is about
500 in Nafion, decreasing the electrolyte concentration fifty-fold only
decreases the dopamine concentration by 10%. The dramatic effect produced
by varying the proton concentration means that the protons, not the
dopamine, compensate the wall charge to establish the interfacial
potential gradient and enhance the radial flux of dopamine. This is
possible because the dopamine, a cationic amine, is heavily ion paired to
the sulfonic acid sites. With a dielectric constant of 20, substantial
ion pairing can be anticipated in Nafion. Ion pairing may explain why the
flux of cationic amines is lower than neutral hydroquinone as can be seen
with reference to FIGS. 4A and 4B which show 6m values for neutron-track
etched polycarbonate/Nafion composites. FIG. 4A shows 6m versus log(d),
where d is the pore diameter. 6m increases above the values for bulk
Nafion as d approaches 30 nm. The concentrations are 2 mM redox species
and 0.1 M electrolyte for RuN+--Ruthenium (H) hexamine (quadrature),
H2Q--Hydroquinone (Δ,∇), DOP+--Dopamine (O), and
FerN+--Trimethylamminomethyl ferrocene (⋄). The electrolyte is
H2SO4 in all cases except for DOP+ and H2Q(∇).
Lines represent no model and are only intended to indicate the trend in
the data. FIG. 4B shows 6m versus d1, where 4d1 is the surface
area of the pore/volume of Nafion in the pore. As illustrated in FIGS. 6A
and 6B, the slopes in FIG. 4B are indicative of the surface flux, and the
intercept corresponds to the flux in bulk Nafion. Note, all the redox
species except hydroquinone are charged amines, and all have lower flux
than hydroquinone.

Vapor Phase Electrochemistry/Microstructure in Two-Dimensions

[0164]One way to alter microstructure is to reduce the conduction matrix
from three to two-dimensions. A two-dimensional system is made by
sulfonating the nonionic, polymeric insulator between the electrodes of a
microelectrode assembly. Conduction across the surface cannot be studied
in either an electrolyte solution or a pure solvent as the liquid
provides a conductive path between the electrodes. However, by supporting
the microelectrode assembly in an evacuated flask, and injecting hydrogen
or hydrogen chloride and a small amount (:L) water, conduction can be
studied by electrolyzing the gas. In these lower dimensional systems, the
role of the ion exchange site and its concentration, as well as the role
of water in ionic conduction can be studied. Preliminary studies were
performed to study conduction through solvent layers adsorbed from the
vapor phase across the nonionic surface of a microelectrode assembly.
Electrolysis of gas phase solvents required the solvent to adsorb at
greater than monolayer coverage to bridge the gap between the electrodes.
Solvents with high autoprotolysis and acidity constants sustain higher
currents than solvents less able to generate ions. These studies provided
information about gas phase electrochemical detection and systems as well
as atmospheric corrosion.

Composites Formed with Polymerized Microspheres

[0165]To test the generality of flux enhancement by interfacial forces,
composites of Nafion and polymerized polystyrene microspheres were
formed; diameters of 0.11 to 1.5 μm were used. FIGS. 7A and 7B show 6m
of hydroquinone through polystyrene microbead/Nafion composites versus
ratios of surface area of the microbeads to volume of Nafion. In
particular, values of Km found for various ratios of bead surface area
for transport to volume of Nafion for extraction (SA/Vol) are shown for
three different bead diameters. As for the neutron track etched
composites, linear plots were found, at least for the larger sizes, with
intercepts comparable to bulk Nafion. Of these sizes, 0.37 μm beads
exhibited the largest flux enhancement (600%). FIG. 7A shows results for
composites formed with single size beads, where the ratio of surface area
to volume was varied by varying the volume fraction of beads in the
composites. Positive slopes are shown consistent with flux enhancement by
surface diffusion along the surface of the beads. The intercepts are
consistent with transport through bulk Nafion.

[0166]The fraction of microspheres in the composite can be varied and
different sizes mixed to allow a continuous range of SA/Vol. In
particular, FIG. 7B shows results for composites for a range of SA/Vol
with 50% total fraction of Nafion by volume in the film. 6m increases as
SA/Vol increases to about 3.5A105 cm-1, analogous to
1.3A106 cm-1 found for the neutron track etched composites
(FIG. 4A). Scanning electron micrographs of the 50% Nafion, single bead
size composites showed packing of the 0.11 μm beads was different and
may account for the lower 6m values found for d1>3.5A105
cm-1, where 0.11 μm beads were used. FIG. 7B shows results for
composites formed with 50% Nafion by volume. The ratio of surface area to
volume was varied by making composites with beads of one and two sizes.
Flux increases as the ratio of surface area to volume increases to
3.5A105 cm-1; at the highest ratio, the composite contains 0.11
μm beads.

[0167]From the scanning electron micrographs, composites of beads larger
than 0.11 μm exhibit the self-similarity typical of fractal materials.
When ln(6m) for these beads is plotted versus log(d), where d is the bead
diameter, a linear plot with a slope of -0.733 was obtained; 6m versus
d0.733 is shown in FIG. 8. For diffusion on a fractal of finitely
ramified structure (e.g., the Sierpinski gasket), this is the power
dependence expected for diffusion in a two-dimensional system. Thus,
microbead composites exhibit transport typical of fractal diffusion along
the microbead surface. This system confirms that surface diffusion
provides a mechanism of flux enhancement. It also introduces the concept
of fractal transport processes and the importance of surface
dimensionality in ion exchange composites.

[0168]To investigate surface diffusion in other ion exchangers, composites
were formed of protonated poly(vinyl pyridine) and track etched
membranes. From preliminary results, flux enhancements in these
composites increased with d (volume/surface area); see FIG. 9. Such a
dependency may be consistent with a transport rate which varies
monotonically in the radial coordinate. Physically, a non-uniform density
of PVP, produced by interaction with the wall charge, could generate a
radially dependent transport rate.

Thermal Processing of Nafion

[0169]While commercial Nafion is heat cast, a process that yields inverted
micelles, the vast majority of academic studies of Nafion have been
performed on cold cast Nafion which produces normal micelles. A study of
the mechanical properties of Nafion hot cast from organic solvents has
been reported. Attempts have been made to hot cast Nafion films with
microwave heating. In the highly ionic casting solution, the glass
transition temperature of Nafion (105° C.) should be reached as
the water evaporates. Plots of flux as a function of the time microwaved
have a break at approximately 15 minutes. The flux changed by no more
than a factor of three with a decrease in the flux of hydroquinone, and
from preliminary studies, an increase in the flux of
Ru(NH3)63+. This may indicate different transport
mechanisms for the two species in the film. Microwaved, cold cast and
commercial hot cast films have been compared.

Magnetic, Demagnetized, and Nonmagnetic Composites

[0170]Polystyrene coated, 1 to 2 μm Iron oxide (nonpermanent magnetic
material) or organo-Fe (superparamagnetic or ferrofluid or permanent
magnetic) microbeads are available (Bangs Labs or Polyscience) as a 1%
suspension in water, and Nafion (C.G. Processing) is available as a 5%
suspension in alcohol/water (other inert or active polymer coatings
besides polystyrene could be employed as well, and in nonaqueous
environments, it is possible to eliminate the polymer coating completely
if for example, its purpose is normally only to prevent oxidation in an
aqueous environment). This discussion holds for superparamagnetic or
ferrofluid or permanent magnetic or nonpermanent magnetic or
ferromagnetic or ferrimagnetic material microbeads in general. This
discussion also holds for other magnets and other magnetic materials
which include, but are not limited to superconductors, and magnetic
materials based on rare earth metals such as cobalt, copper, iron,
samarium, cerium, aluminum and nickel, and other assorted metal oxides,
or magnetic materials based on neodymium, e.g., magnequench, which
contains iron and boron in addition to neodymium. The polymer coatings
are required for use of these microbeads in an aqueous environment to
prevent oxidation, but in a nonaqueous environment the polymer coating
may not be required. Magnetic composites incorporating organo-Fe material
microbeads are formed by casting appropriate volumes of each suspension
onto an electrode centered inside a cylindrical magnet (5 cm inside
diameter, 6.4 cm outside diameter, 3.2 cm height; 8 lb pull). Once the
solvents evaporate and the magnet is removed, the oriented beads are
trapped in the Nafion, stacked in pillars normal to the electrode
surface. To minimize interbead repulsion, pillars form by stacking the
north end of one bead to the south end of another; to minimize
interpillar repulsion, the pillars arrange in a roughly hexagonal array.
These aligned composites were formed with microbead fractions of
≦15%. Aligned composites were compared to other composites:
unaligned composites--formed as above but with Iron oxide microbeads and
without the magnet; nonmagnetic composites--formed with 1.5 μm
nonmagnetic polystyrene beads; simple Nafion films; and demagnetized
composites--aligned composites that were demagnetized. Demagnetized
composites had the pillared structure, but it is not clear if they were
fully demagnetized. Nonmagnetic composites had a coral-like structure
(i.e., they do not form pillars). Note, composites may be formed wherein
at least one component is reversibly changeable between a paramagnetic
form and a diamagnetic form with, for example, a temperature variation
with or without the presence of an externally applied magnetic field.

Magnetic Composites

Electrochemical Studies of Magnetic Composites

[0171]The composite was equilibrated in a solution of 1 mM electro-active
species and 0.1 M electrolyte. The mass transport-limited current for the
electrolysis of the redox species through the composite (imeas) was
then determined by steady-state rotating disk voltammetry at several
different rotation rates (w). A plot of imeas-1 versus w-1
yielded a slope characteristic of transport in solution, and an intercept
characteristic of transport through the composite as:

In Equation (3), n is the number of electrons, F is the Faraday constant,
A is the electrode area, c* and Dsoln- are the concentration and
diffusion coefficient of the redox species in solution, respectively,
< is the kinematic viscosity, l is the composite thickness, 6 is the
partition coefficient of the redox species, m is the mass transport rate
of the redox species in the composite, and E is the porosity of the
composite. The partition coefficient, 6, is the ratio of the equilibrium
concentration in the ion exchange portion of the composite to the
solution concentration, in the absence of electrolysis. Equation (3) is
appropriate for rate-limiting transport perpendicular to the electrode.
This is ensured by choosing l and
D1/3solnw-1/2<1/6 large compared to the
microstructural dimensions of the composite, and is verified by the
slope. Then, the composite can be treated as homogeneous with an
effective 6m, and microstructural effects can be ascertained with
rotating disk studies. Cyclic voltammetry yielded quantitative
information for scan rates, v, sufficient to contain the transport length
within the composite. For a reversible couple, the peak current,
ipeak, is

ipeak=0.4463(nF)1/2[v/RT]1/2, (4)

where R is the gas constant and T is the temperature. When both rotating
disk and cyclic voltammetry data are obtainable, 6 and m are separable
because of their different power dependencies in Equations (3) and (4).

[0172]The flux of redox species through magnetic composites is enhanced in
proportion to the absolute value of the difference in the magnetic
susceptibilities of the products and reactants of the electrolysis. From
cyclic voltammetry, the ΔEp observed for reversible species,
whether paramagnetic or diamagnetic, was little changed, but E0.5
was shifted, where E0.5 is the average of the anodic and cathodic
peak potentials, and is a rough measure of the free energy of the
electron transfer reaction. For a quasireversible, diamagnetic species
which passed through a radical intermediate, dramatic changes in
ΔEp were found. The shifts and peak splittings were consistent
with the stabilization and the concentration of the paramagnetic species.
Results are summarized below.

[0174]In these examples, as in general, when flux of redox species through
the magnetic composite was compared to flux through either Nafion films
or composites formed with nonmagnetic beads, the flux was enhanced. In
general, we find the flux enhancement is not dependent on whether the
electrolysis is converting a diamagnetic to a paramagnetic species or a
paramagnetic to a diamagnetic species, but that the enhancement increases
as the absolute value of the difference in the molar magnetic
susceptibility of the product and reactant.

[0175]To further investigate paramagnetic (Ru(NH3)63+, 6m
values were found for magnetic and nonmagnetic composites made with
various fractions of beads. Results are shown in FIG. 10. First, in FIG.
10 the flux of Ru(NH3)63+ increased strongly with the
fraction of magnetic beads, but not with the fraction of nonmagnetic
beads. Second, since the enhancement is not linear with the magnetic bead
fraction, the enhancement was not due to either a simple concentration
increase of the paramagnetic species about each bead or a simple increase
in surface diffusion associated with more pillars at higher bead
concentration. (Data are equally well linearized with correlation
coefficient>0.99 as either In[6m] versus percent beads, or 6m versus
volume of Nafion/surface area of the beads. Plots of both showed
intercepts comparable to 6m for simple Nafion films.) Third,
substantially higher flux was achieved with the magnetic beads than with
the same fraction of nonmagnetic beads.

[0176]Magnetohydrodynamic models neither account for the discrimination
between paramagnetic and diamagnetic species by the magnetic composites,
nor do they predict the shape of the curve shown in FIG. 10.

[0177]Electrochemical flux of various redox species from solution through
either composites or films to the electrode surface was determined by
cyclic and steady-state rotating disk voltammetry. Electrochemical flux
of species through the composites is parameterized by 6 and m, where 6 is
the extraction coefficient of the redox species from solution into the
composite, and m (cm2/s) is its effective diffusion coefficient. For
steady-state rotating disk voltammetry, the parameterization is 6m
(determined from the intercept of a Koutecky Levich plot [12a]), and for
cyclic voltammetry, the parameterization is 6 m1/2 (extracted from
the slope of peak current versus the square root of the scan rate (20 to
200 mV/s) [12b]). All measurements were made in solutions containing 1 to
2 mM redox species at a 0.45 cm2 glassy carbon electrode. The
electrolyte was 0.1 M HNO3, except for the reduction of
Co(bpy)32+ (0.2 M Na2SO4) and for the oxidation of
Co(bpy)32+ and reduction of Co(bpy)33+ (0.1 M sodium
acetate/acetic acid buffer at pH=4.5). Anionic ferricyanide was not
detected electrochemically through the anionic Nafion films and
composites, consistent with defect-free layers. All potentials were
recorded versus SCE.

[0178]First, 6m values were determined for the oxidation of paramagnetic
Ru(NH3)63+ to diamagnetic Ru(NH3)62+
through magnetic and nonmagnetic composites as the bead fraction was
increased. |Δχm|=1,880A10-6 cm3/moles[13]. From
FIG. 10 , 6m for the nonmagnetic composites varies little with bead
fraction, while 6m for the magnetic composites increases superlinearly by
several fold.

[0179]Second, 6m1/2 values were determined for various redox
reactions for magnetic composites, nonmagnetic composites, and Nafion
films. Exclusive of any magnetic field effects, electrochemical flux
through Nafion can be altered by the size, charge, and hydrophobicity of
the transported species, interaction and binding with the exchange sites,
and intercalation into the hydrated and perfluorinated zones of the
Nafion. To minimize effects not related to interactions between the redox
moieties and the magnetic beads, 6 m1/2 values for the magnetic and
nonmagnetic composites are normalized by 6m1/2 for the Nafion films.
The normalized 6m1/2 values are plotted in FIG. 11 versus
|Δχm| for the various redox reactions [13], [14]. FIG. 11
illustrates the relative flux of redox species on the y-axis, where the
maximum cyclic voltammetric current for a composite with magnetic
microbeads is normalized by the maximum cyclic voltammetric current for a
Nafion film containing no magnetic material. The ratio is the flux
enhancement. On the x-axis is the absolute value of the difference in the
molar magnetic susceptibilities of the products and reactants of the
electrolysis, |)Pm|. The composites contain 15% magnetic microbeads
and 85% Nafion by volume. The redox species are numbered as follow, where
the reactant products are listed sequentially: (1) hydroquinone to
benzoquinone; (2) Cr(bpy)33+ to Cr(bpy)32+; (3)
Ru(bpy)32+ to Ru(bpy)33+; (4)
Ru(NH3)63+ to Ru(NH3)62+; (5)
Co(bpy)32+ to Co(bpy)31+; (6) CO(bpy)32+ to
Co(bpy)33+; and (7) Co(bpy)33+ to
Co(bpy)32+. All redox species are 1 mM to 2 mM. Film
thicknesses are 3.6 micrometers to 3.8 micrometers. For the nonmagnetic
composites, the normalized 6m1/2 values are independent of
|Δχm|. This suggests the normalization is effective in
minimizing steric and electrostatic differences in the interactions of
the various redox species with Nafion. For the magnetic composites,
normalized 6m1/2 increases monotonically with |Δχm|,
with the largest enhancements approaching 2000%.

[0180]The logarithmic increase of electrochemical flux in FIG. 11 with
|Δχm| is consistent with a free energy effect of a few
kJ/mole. Effects of this magnitude have not been generated in uniform,
macroscopic magnetic fields. Strong, non-uniform magnetic fields
established over short distances (a few nanometers) at the interface
between Nafion and magnetic microbeads could produce local effects of
this magnitude. Magnetic concepts appropriate to uniform macroscopic
magnetic fields and to molecular magnetic interactions are not applicable
to this system, and instead, a microscopic parameterization is necessary.
Establishing sufficiently strong and nonuniform local magnetic fields at
interfaces in microstructured systems makes it possible to orchestrate
chemical effects in micro-environments which cannot otherwise be achieved
with uniform fields applied by large external magnets.

Cyclic Voltammetric Peak Splittings for Quasireversible Species

[0181]Peak splittings in cyclic voltammetry are used to determined
heterogeneous electron transfer rates. FIGS. 12A and 12B show cyclic
voltammetric results for the reversible species Ru(NH3)63+
and Ru(bpy)32+, respectively. Cyclic voltammograms at 100 mV/s
are shown for Ru(NH3)63+ (FIG. 12A) and
Ru(bpy)32+ (FIG. 12B) for magnetic composites, Nafion films,
and the bare electrode. Cyclic voltammetric results are shown for the
reduction of paramagnetic Ru(NH3)63+ in FIG. 12A. The
concentration of the redox species is 1 mM, and the electrolyte is 0.1 M
HNO3; the reference is an SCE; and the films are 3.6 μm thick.
For both species, when E0.5 is compared for the magnetic composite
and the Nafion films, the shift in E0.5 is to positive potentials.
The electron transfer kinetics for Ru(NH3)63+ are fairly
strong with k0>0.2 cm/s. Note that the peak splittings for the
magnetic composites and Nafion film are similar, consistent with the
resistance of the two layers being similar. Similar peak splittings are
also observed for Ru(bpy)32+, as shown in FIG. 12B. Therefore,
when compared to the Nafion films, the magnetic composites have little
effect on the rate of electron transfer of reversible species.

[0182]In particular, FIG. 12C shows cyclic voltammograms at 100 mV/s for 1
mM hydroquinone in 0.1 M HNO3 for magnetic composites, nonmagnetic
composites, Nafion films, and the bare electrode. The films are 3.6 μm
thick. It is observed in the voltammogram of FIG. 12C that the peak
splitting is almost doubled for the magnetic composite compared to the
Nafion film. The question arises as to whether the enhanced peak
splitting is consistent with the stabilization of the paramagnetic
semiquinone intermediate in the two electron/two proton oxidation. In
FIG. 12C, voltammograms are shown at 0.1 V/s for hydroquinone, a
diamagnetic species that undergoes quasireversible, two electron/two
proton oxidation to diamagnetic benzoquinone while passing through a
radical, semiquinone intermediate. The voltammograms for the Nafion film
and the nonmagnetic composites are fairly similar, with ΔEp
values of 218 and 282 mV, respectively. For the magnetic composite,
ΔEp=432 mV, or twice that of the Nafion film. From the results
for the reversible couples above, this is not due to a higher resistance
in the magnetic composites. The asymmetry in the peak shifts compared to
the other three systems shown in FIG. 12C also argues against a
resistance effect. (Note that the interpretation of the kinetics can be
complicated by the proton concentration. However, there is no reason to
think the concentration is drastically different in the magnetic and
nonmagnetic composites.) The peak shift may be due to the stabilization
of the paramagnetic semiquinone intermediate.

[0183]While the hydroquinone electrolysis is too complex to interpret
cleanly, it does raise the interesting question of whether
quasireversible electron transfer rates can be influenced by an applied
magnetic field. Reversible rates will not be affected, but it is not
clear what would happen with quasireversible rates. There are many
quasireversible electron transfer species uncomplicated by homogeneous
kinetics and disproportionation reactions which can be used to better
resolve this question. If the kinetics of quasireversible processes can
be influenced by magnetic fields, numerous technological systems could be
improved.

Cyclic Voltammetric Peak Shifts

[0184]When magnetic composites and Nafion films were compared,
voltammograms taken at 0.1 V/s for the reversible species exhibited no
change in ΔEp. However, the peak potential for reduction,
Epred, for Ru(NH3)63+was shifted 14 mV positive.
Similarly, the oxidation potential peak, Epox, for
Ru(bpy)32+was shifted 64 mV positive. Shifts of E0.5 while
ΔEE is unchanged are consistent with one species being held
more tightly in the composites, and thereby, having a lower diffusion
coefficient. In general, a shift in potential of approximately +35 mV is
observed for all reversible redox species, whether the electron transfer
process converts the redox species from diamagnetic to paramagnetic or
paramagnetic to diamagnetic. Larger potential shifts are observed with
less reversible electron transfer processes. Shifts as large as 100 mV
have been observed. (Note that for the film thicknesses used herein ( 3.6
μm) and a scan rate of 0.1 V/s, m≦10-8 cm2/s is
needed for the diffusion length to be confined within the film during the
sweep. Since m is not known in these systems, it is not clear whether the
voltammetric results also probe behavior at the composite/solution
interface.)

[0185]The above discussion further shows that interfacial gradients other
than concentration and electric potential, e.g., magnetic gradients, can
be exploited effectively in microstructured matrices. In composites
formed with magnetic materials, locally strong (and nonuniform) magnetic
fields could alter transport and kinetics. The influence of the magnetic
field on species in composites may be substantial because the species are
concentrated in a micro-environment, where the distance between the field
source and chemical species is not large compared to the field decay
length. Magnetic composites were made by casting films of polystyrene
coated magnetic beads and the perfluorinated, cation exchange polymer,
Nafion, onto an electrode. Approximately 1 μm diameter magnetic beads
were aligned by an external magnet as the casting solvents evaporated.
Once the solvents evaporated and the external magnet was removed, the
beads were trapped in the Nafion, stacked as magnetic pillars
perpendicular to the electrode surface.

[0186]Preliminary voltammetric studies comparing the magnetic composites
to simple Nafion films yielded several interesting results. First, flux
of redox species through magnetic microbead composites is enhanced
compared to flux through composites formed with nonmagnetic microbeads.
Second, for species which underwent reversible electron transfer (i.e.,
Ru(NH3)63+ and Ru(bpy)32+), the cyclic
voltammetric peak potential difference (ΔEp) was unaffected,
but the average of the peak potentials (E0.5) shifted consistent
with the stabilization of the paramagnetic species. Third, hydroquinone
oxidation was quasireversible and proceeded through paramagnetic
semiquinone. For hydroquinone at 0.1 V/s, voltammograms for the magnetic
composites exhibited a 40 mV positive shift of E0.5 and a
ΔEp twice that of Nafion. The potential shifts and flux
enhancements, while consistent with concentration and stabilization of
the paramagnetic form of the redox couples, are as yet unexplained.

[0187]Electrochemical flux of ions and molecules through magnetic
composites formed of Nafion ion exchange and polystyrene coated Iron
oxide particles has been observed to be as much as twenty-fold higher
than the flux through simple Nafion films. Flux enhancements have been
observed with increasing difference in the magnetic susceptibility of the
halves of the redox reaction.

[0188]A passive, magnetic composite may be used to enhance the flux of
oxygen at the cathode in a fuel cell. Oxygen has two unpaired electrons,
and is therefore susceptible to this magnetic field in the same way as
described in the experiments above. If oxygen is consistent with the
observations made thus far for other ions and molecules, the
electrochemical flux of oxygen to a magnetically modified cathode can be
enhanced by approximately 500% as compared to a nonmagnetic cathode (FIG.
13). Such an enhancement would be comparable to that achieved by
pressurization to 5 atmospheres at the cathode.

[0189]Based on the above discussion, it is possible to predict a roughly
five-fold flux enhancement of oxygen through a 15% magnetic/Nafion
composite over Nafion. This is understood by considering the fluxes
through magnetic/Nafion composites and Nafion films of the seven redox
species listed in the upper left hand corner of FIG. 13 and are the same
species as listed in FIG. 11. The fluxes were determined by cyclic
voltammetry. The flux ratio for magnetic composites to Nafion films is
the y-axis and the absolute value of the difference in the molar magnetic
susceptibilities χm|) of products and reactants of the
electrolysis reaction is the x-axis of FIG. 13, respectively. (The larger
the value of χm, the more susceptible a species is to
interaction with a magnetic field.) From FIG. 13, the flux increases
exponentially as |χm| increases. For the most extreme case, the
flux is increased about twenty-fold. For the reduction of oxygen to
water, |χm|≈3500A10-6 cm3/mole. This point on
the x-axis is extrapolated to therefore suggest that the flux enhancement
for oxygen in the magnetic composite will approach five-fold.

[0190]Experiments have been conducted with Nafion composites of up to 15%
Iron oxide particle beads. FIG. 14 shows a curve of the increase in flux
based on the percentage of magnetic beads. The dotted line on FIG. 14 is
the projected effect on flux of higher bead concentrations.

[0191]For paramagnetic species, the flux through the magnetic composites
increases as the fraction of magnetic beads increases. In FIG. 14, the
flux of Ru(NH3)63+through magnetic bead/Nafion composites
( ) increases as the fraction of magnetic beads in the composite is
increased to 15%. Larger enhancements may be possible with higher bead
fraction composites or composites formed with magnetic beads containing
more magnetic material. Compared to a simple Nafion film (quadrature),
the flux is 4.4 fold larger. Ru(NH3)63+ is less
paramagnetic than oxygen. For comparison, composites formed with
nonmagnetic polystyrene beads (◯) were examined; these
exhibited no flux enhancement as the bead fraction increased. The line
shown on the plot is generated as a logarithmic fit to the data for the
magnetic composites. It illustrates the flux enhancement that might be
found for composites formed with a higher fraction of magnetic beads. The
extrapolation suggests that at 30% magnetic beads, the flux through the
magnetic composites of Ru(NH3)63+might approach twenty
times its value in simple Nafion films. As oxygen is more paramagnetic
than Ru(NH3)63+even larger enhancements might be
anticipated for oxygen.

Oxygen Susceptibility to Magnetic Composites and Magnetic Concepts

[0192]Paramagnetic molecules have unpaired electrons and are drawn into
(aligned by) a magnetic field (i.e., a torque will be produced; if a
magnetic field gradient exists, magnetic dipoles will experience a net
force). Radicals and oxygen are paramagnetic. Diamagnetic species, with
all electrons paired, are slightly repelled by the field; most organic
molecules are diamagnetic. (Metal ions and transition metal complexes are
either paramagnetic or diamagnetic.) How strongly a molecular or chemical
species responds to a magnetic field is parameterized by the molar
magnetic susceptibility, Pm (cm3/mole). For diamagnetic
species, Pm is between (-1 to -500)A10-6 cm3/mole, and is
temperature independent. For paramagnetic species, Pm ranges from 0
to +0.01 cm3/mole, and, once corrected for its usually small
diamagnetic component, varies inversely with temperature (Curie's Law).
While ions are monopoles and will either move with or against an electric
field, depending on the sign of the potential gradient (electric field),
paramagnetic species are dipoles and will always be drawn into (aligned
in) a magnetic field, independent of the direction of the magnetic
vector. A net force on a magnetic dipole will exist if there is a
magnetic field gradient. The magnetic susceptibilities of species
relevant to this proposal are summarized below.

[0193]Magnetic field effects were observed in electrochemical systems.
Because electrochemistry tends to involve single electron transfer
events, the majority of electrochemical reactions should result in a net
change in the magnetic susceptibility of species near the electrode.
Little has been reported, however, in electrochemistry on magnetic
fields. What has been reported relates to magnetohydrodynamics.
Magnetohydrodynamics describes the motion of the charged species (i.e.,
an ion) perpendicular to the applied magnetic field and parallel to the
applied electric field(Lorentz force). In the composites described
herein, the magnetic field, the direction of motion, and the electric
field were all normal to the electrode. Because magnetohydrodynamics (see
FIGS. 1-3) does not predict a motion dependence on the magnetic
susceptibility of the moving species and requires that all the field and
motion vectors are perpendicular (i.e., for magnetic effects), the
effects described here are unlikely to be macroscopic magnetohydrodynamic
effects.

Graded Density Composites

[0194]The following protocol is used to form density layers on electrodes
with the density layers parallel to the electrode surface or other
surface: A solution of a copolymer of sucrose and epichlorhydrin
(commercially available as Ficoll and used to make macroscopic graded
density columns for separations of biological cells by their bouancy) are
made in water at concentrations varying from a few percent to 50% by
weight. The viscosity of the solution is a monotonic function of the
weight percent polymer. Small volumes of polymer solution (5 to 100
microliters) are pipetted onto to an electrode surface and the electrode
spun at 400 rpm for two minutes; this creates a single polymer layer. By
repeating this process with polymer solutions of different
concentrations, a graded interface with density and viscosity varied as a
function of the composition of the casting solution can be created. The
thickness of each step in the staircase structure depends on the number
of layers cast of a given concentration, and can range from 200 nm to
several micrometers.

[0195]A similar structure with graded layers of ion exchange sites in ion
exchange polymers can be formed by (1) spin casting a mixture of density
gradient polymer and ion exchange polymer on the electrode or other
surfaces as described above; (2) forming a density graded layer of
density polymer first, and then adsorbing the ion exchange polymer into
the matrix; (3) spin coating layers of ion exchange polymers on surfaces
from solution of different concentrations. It should be possible to cast
such layers, and then peel them off surfaces to form free standing films.
Such films would have utility in controlling solvent transport across
electrochemical cells, including fuel cells.

[0196]A protocol is proposed to form density layers on electrodes with the
density layers perpendicular to the electrode surface or other surface.
Electrodes and surfaces can be envisioned in which more than one gradient
is established on the surface for purposes of separating molecules in
more than one spatial and temporal coordinate and by more than one
property. One example is to form composites with a magnetic gradient in
one coordinate and a density gradient in the other. These materials could
be formed by creating a magnetic gradient perpendicular to the electrode
surface by placing magnetic beads on an electrode or surface and allowing
the composite to be cast in a nonuniform field, where the external magnet
is aligned so the beads are on the surface but not in columns
perpendicular to the surface. A density payer could be cast (as opposed
to spun coat) by pipetting small volumes of different concentration of
density gradient polymer and/or ion exchange polymer and allowing the
solvents to evaporate, thereby building up a graded layer parallel to the
electrode surface. Once the entire layer is cast, the external magnet can
be removed if the magnetic material is superparamagnetic, and left in
place if the magnetic material is paramagnetic.

[0197]These would be fairly sophisticated composites, and complex to
understand, but unusual flux enhancements and separations should be
possible in several dimensions. It should be possible to design even more
complex structures than these.

Modified Ion Exchangers

[0198]The surface of the magnetic microbeads have ion exchange groups on
them which would allow ready chemical modification, e.g., like coating
with a magnetically oriented liquid crystal for a local flux switch.
Examples of such modified structures may have use in the quest to build
microstructured devices and machines.

Applications

General Applications

[0199]FIG. 15A shows a simplified representation which will be used to
describe how magnetic microboundaries 10a, 10b 10c influence a standard
electrochemical process. Here, a substrate 20 with a surface 24 serves as
a conductor and hence can electrically conduct like a metal, a
semiconductor or a superconductor. Substrate 20 is maintained at a first
potential V1. Two different phases of materials 30a and 30b have two
different magnetic fields, i.e., are in two different magnetic phases,
phase 1 and phase 2 and are applied to surface 24 of substrate 20. Since
materials 30a and 30b have different magnetic fields, boundary regions 33
have magnetic gradients. Boundary regions 33 are not necessarily sharp or
straight, but the magnetic field of material 30a smoothly changes into
the magnetic field of material 30b according to electromagnetic boundary
conditions. Therefore, width t represents an average width of boundaries
33. Width t should be approximately between a few nanometers to a few
micrometers and preferably between one nanometer and approximately 0.5
micrometers. Boundary regions 33 are separated from each other by varying
distances and S represents the average of these distances. The effect of
varying distances S will be described below.

[0200]Particles M have a magnetic susceptibility χm and are in an
electrolyte 40 which is at a potential V2 due to an electrode 50. This
makes a potential difference of V between electrolyte 40 and substrate 20
(substrate 20 can effectively act as a second electrode). Boundary
regions 33 are paths which can pass particles M. Particles M are then
either driven electrically or via a concentration gradient toward
substrate 20. Once particles M reach substrate 20, they either acquire or
lose electrons, thereby turning into particles N with magnetic
susceptibility Pn. The absolute value of the difference between the
magnetic susceptibilities of phase 1 and phase 2 is a measure of the
magnitude of the magnetic gradient in region 33 and will be referred to
as the magnetic gradient of boundary region 33. It will be shown below
that the flux of particles M increases approximately exponentially with
respect to increasing the magnetic gradient of boundary region 33 with
materials 30a and 30b when compared to the flux without materials 30a and
30b. This increase in flux can be over a factor of 35-fold or 3500%
resulting in significant improvements in efficiency of many
electrochemical processes.

[0201]Specific examples of electrochemical systems where magnets might
improve an electrochemical cell or process include: chloralkali
processing, electrofluoridation, corrosion inhibition, solar and
photocells of various types, and acceleration of electrochemical
reactions at the electrode and in the composite matrix. Potential shifts
of E0.5 are always observed and suggest an energy difference is
generated by the magnetic fields and gradients in the composites;
generically, this could improve performance of all electrochemical energy
devices, including fuel cells, batteries, solar and photocells. In other
application, sensors, including dual sensors for parametric species;
optical sensors; flux switching; and controlled release of materials by
control of a magnetic field, including release of drugs and biomaterials.
There may also be applications in resonance imaging technology.

[0202]Boundaries 33 do not have to be equally spaced and do not have to
have equal widths or thicknesses t. Materials 30a and 30b can be liquid,
solid, gas or plasma. The only restriction is that a boundary 33 must
exist, i.e., materials 30a and 30b must have two different magnetic
fields to create the magnetic gradient within the width t. Magnetic
gradient of region 33 can be increased by (1) increasing the magnetic
content of the microbeads; (2) increasing the bed fraction in the
composite; (3) increasing the magnetic strength of the beads by improving
the magnetic material in the beads; and (4) enhancing the field in the
magnetic microbeads by means of an external magnet. In general, the flux
of particles M and N is correlated with magnetic susceptibility
properties, Pm and Pn. The above phenomena can be used to
improve performance of fuel cells and batteries.

[0203]FIG. 15B shows apparatus 80 which corresponds to any of the above
discussed embodiments as well as the embodiments shown in FIG. 16 or
after. Some of the embodiments in their implementation require the
presence of a magnetic field such as that produced by electomagnet 70 and
some of the embodiments do not require electromagnet 70, although they
can do so. Apparatus 80 corresponds to, for example, some embodiments of
the magnetically modified electrode, the fuel cell, the battery, the
membrane sensor, the dual sensor, and the flux switch. Electromagnet 70
can be any source of a magnetic field. Electromagnet 70 can also be used
in the above discussed methods of forming the composite magnetic
materials that require the presence of an externally applied magnetic
field. Electromagnet 70 can be controlled by controller 72 to produce a
constant or oscillating magnetic field with power supplied by power
supply 74.

[0204]FIG. 16 shows another simplified diagram showing a second
manifestation of the above described phenomenon and hence a second broad
area of application. Namely, FIG. 16 shows a separator 60 which separates
a first solution 62a from a second solution 62b. Here, there is no
electrode or conductive substrate 20. Solution 62a has at least two
different types of particles M1 and M2 with two different
magnetic susceptibilities χm1 and χm2, respectively.
Once particles M1 or M2 drift into an area near any one of
boundaries 33, they are accelerated through the boundaries 33 by the
magnetic gradient therein. Here, χm1 is greater than
χm2, which causes the flux of particles M, through separator 60
to be greater than the flux of particles M2 through separator 60.
This difference in flux can again be over a factor of 3500%, and may
somewhat cancel out any difference in acceleration due to different
masses of particles M, and M2. Consequently, if the above process is
allowed to proceed long enough, most of the particles M, will have passed
through separator 60 before particles M2, thereby making first
solution 62a primarily made up of particles M2 and second solution
62b primarily made up of particles M1. Note, separation of particles
M1 and M2 may require some special tailoring of the separator
60 and also relies on how much time is allowed for particles M, and
M2 to separate. In an infinite amount of time, both particles M, and
M2 may cross separator 60. Particle size may also have a bearing on
the ultimate separation of particles M, and M2 by separator 60.

[0205]The above discussion with respect to FIG. 16 involves two types of
particles, M1 and M2, but the discussion also holds for any
number of particles. Consider, for example, solution 62a having particles
M1, M2, M3 and M4 with susceptibilities χm1,
χm2, χm3 and χm4, respectively. If
χm1>χm2>χm3>χm4, then
M1 would pass more easily through separator 60, followed by M2,
M3, and M4. The greater the difference between magnetic
susceptibilities, the better the separation. The above phenomenon can be
used to improve performance of fuel cells and batteries. Other
applications include separation technology in general, chromatographic
processes--includes higher transition metal species (lanthanides and
actinides), and photography.

[0206]In the above discussion with respect to FIGS. 15 and 16, the greater
the number of boundary regions 33 per unit area (i.e., the smaller S),
the greater the effects due to the presence of boundary regions 33
macroscopically manifest themselves. S can vary from fractions of a
micrometer to hundreds of micrometers. In quantum systems with smaller
structures, S is further reduced to less than approximately 10 nm.

[0207]Design paradigms are summarized below to aid in tailoring composites
for specific transport and selectivity functions. [0208]Forces and
gradients associated with interfaces, which are of no consequence in bulk
materials, can contribute to and even dominate the transport processes in
composites. [0209]Increasing the microstructure of composites can enhance
the influence of interfacial gradients. [0210]The closer a molecule or
ion is placed to the interface, the stronger the effect of the
interfacial field on the chemical moiety. Systems should be designed to
concentrate molecules and ions near interfaces. [0211]The ratio of
surface area for transport to volume for extraction parameterizes surface
transport. [0212]Fields in a microstructural environment can be
non-uniform, but locally strong. [0213]Strong but short range
electrostatic and magnetic fields are better exploited in microstructured
environments than in systems with externally applied, homogeneous fields.
[0214]Vectorial transport is plumbed into microstructured matrices by
coupling two or more field or concentration interfacial gradients; the
largest effects will occur when the gradients are either perpendicular or
parallel to each other. [0215]Control of surface dimensionality
(fractality) is critical in optimizing surface transport in composites.

[0216]Several advantages are inherent in ion exchange composites over
simple films. First, composites offer properties not available in simple
films. Second, composites are readily formed by spontaneous sorption of
the ion exchanger on the substrate. Third, while surfaces dominate many
characteristics of monolayers and composites, three-dimensional
composites are more robust than two-dimensional monolayers. Fourth,
interfaces influence a large fraction of the material in the composite
because of the high ratio of surface area to volume. Fifth, composites
offer passive means of enhancing flux; external inputs of energy, such as
stirring and applied electric and magnetic fields, are not required.
Sixth, local field gradients can be exploited in composites because the
fields and molecular species are concentrated in a micro-environment
where both the decay length for the field and the microstructural feature
length are comparable. In some of the composites, the field may be
exploited more effectively than by applying an homogeneous field to a
cell with an external source.

Specific Examples

Fuel Cells

[0217]Hence it would be very beneficial to achieve high efficiency
compressor/expander power recovery technology. One way to improve the
efficiency of the compressor/expander would be to reduce the pressure
requirement. If a passive pressurization process could be provided within
the fuel cell itself, at no cost to the power output of the fuel cell,
power production from present day fuel cells would be increased by
approximately 20%.

[0218]Magnetically modified cathodes may reduce the need for
pressurization as oxygen is paramagnetic. The field may also alter oxygen
kinetics. Potential shifts of +35 mV to +100 mV represent a 5% to 15%
improvement in cell efficiency, a comparable savings in weight and
volume. Also, in fuel cells, as hydrated protons cross the cell, the
cathode floods and the anode dehydrates. Water transport may be throttled
by composite separators of graded density and hydration.

Membrane Sensors

[0219]Membrane sensors for the paramagnetic gases O2, NO2, and
NO (recently identified as a neurotransmitter) could be based on magnetic
composites where enhanced flux would reduce response times and amplify
signals. Sensors for other analytes, where oxygen is an interferant,
could distinguish between species by using dual sensors, identical except
one sensor incorporates a magnetic field. Examples of these sensors could
be optical, gravimetric, or electrochemical, including amperometric and
voltammetric. In sensors, the measured signal is proportional to the
concentration of all species present to which the sensor applies. The
presence of a magnetic component in the sensor will enhance sensitivity
to paramagnetic species. Through a linear combination of the signal from
two sensors, similar in all respects except one contains a magnetic
component, and the sensitivity of the magnetic sensor to paramagnetic
species (determined by calibration), it is possible to determine the
concentration of the paramagnetic species. In a system where the sensors
are only sensitive to one paramagnetic and one diamagnetic species, it is
possible to determine the concentration of both species.

Flux Switches

[0220]As nanostructured and microstructured materials and machines develop
into a technology centered on dynamics in micro-environments, flux
switches will be needed. Externally applied magnetic fields can actuate
flux switches using electrodes coated with composites made of
paramagnetic polymers and iron oxide or other non-permanent magnetic
material, or internal magnetic fields can actuate flux switches using
electrodes coated with composites made of electro-active polymers or
liquid crystals, where one redox form is diamagnetic and the other is
paramagnetic, and organo-Fe or other superparamagnetic or ferro-fluid
materials or permanent magnetic or aligned surface magnetic field
material. Also, an external magnet can be used to orient paramagnetic
polymers and liquid crystals in a composite containing paramagnetic
magnetic beads. Enhanced orientation may be possible with magnetic beads
containing superparamagnetic of ferrofluid materials.

Batteries

[0221]Batteries with increased current densities and power, as well as
decreased charge and discharge times may be made with magnetic bead
composites. The improvements would be driven by flux enhancement,
transport enhancement, electron kinetic effects, or by capitalizing on a
potential shift. The required mass of microbeads would little affect
specific power. Since magnetic fields can suppress dendrite formation,
secondary battery cycle life may be extended. Examples include
magnetically modified electrodes. The magnetic coatings may be on the
electrodes or elsewhere in the battery structure.

[0222]FIG. 17 is a short summary of steps involved in a method of making
an electrode according to two embodiments of the invention. In one
embodiment, the method is a method of making an electrode with a surface
coated with a magnetic composite with a plurality of boundary regions
with magnetic gradients having paths to the surface of the electrode
according to one embodiment of the invention. In particular step 702
involves mixing a first solution which includes a suspension of at least
approximately 1 percent by weight of inert polymer coated magnetic
microbeads containing between approximately 10 percent and approximately
90 percent magnetizable polymer material having diameters at least about
0.5 micrometers in a first solvent with a second solution of at least
approximately 2 percent by weight of ion exchange polymers in a second
solvent to yield a mixed suspension. Step 708 then involves applying the
mixed suspension to the surface of the electrode. The electrode is
arranged in a magnetic field of at least approximately 0.05 Tesla,
wherein the magnetic field has a component oriented approximately along
the normal of the electrode surface and preferably is entirely oriented
approximately along the normal of the electrode surface. Step 714 then
involves evaporating the first solvent and the second solvent to yield
the electrode with a surface coated with the magnetic composite having a
plurality of boundary regions with magnetic gradients having paths to the
surface of the electrode.

[0223]Step 702 can include mixing the first solution which includes a
suspension of between approximately 2 percent and approximately 10
percent by weight of inert polymer coated magnetic microbeads with the
second solution. Alternatively, step 702 can include mixing the first
solution which includes inert polymer coated magnetic microbeads
containing between 50 percent and 90 percent magnetizable polymer
material with the second solution. Alternatively, step 702 can include
mixing the first solution which includes inert polymer coated magnetic
microbeads containing 90 percent magnetizable polymer material with the
second solution.

[0224]In addition, step 702 can include mixing a first solution which
includes a suspension of at least approximately 5 percent by weight of
inert polymer coated magnetic microbeads containing between approximately
10 percent and approximately 90 percent magnetizable polymer material
having diameters ranging between approximately 0.5 micrometers and
approximately 12 micrometers. Alternatively, step 702 can include mixing
a first solution which includes a suspension of at least approximately 5
percent by weight of inert polymer coated magnetic microbeads containing
between approximately 10 percent and approximately 90 percent
magnetizable polymer material having diameters ranging between
approximately 1 micrometer and approximately 2 micrometers.

[0225]Mixing step 702 can also involve mixing a first solution which
includes a suspension of at least approximately 5 percent by weight of
inert polymer coated magnetic microbeads containing between approximately
10 percent and approximately 90 percent magnetizable polymer material
having diameters at least 0.5 micrometers in a first solvent with a
second solution of at least approximately 5 percent by weight of Nafion
in a second solvent to yield the mixed suspension.

[0226]Step 702 can involve mixing a first solution which includes a
suspension of at least approximately 5 percent by weight of inert polymer
coated magnetic microbeads containing between approximately 10 percent
and approximately 90 percent organo-Fe material having diameters at least
0.5 micrometers in a first solvent with a second solution of at least
approximately 5 percent by weight of ion exchange polymers in a second
solvent to yield the mixed suspension.

[0227]Step 708 can include applying approximately between 2 percent and
approximately 75 percent by volume of the mixed suspension to the surface
of the electrode. Alternatively, step 708 can include applying between 25
percent and 60 percent by volume of the mixed suspension to the surface
of the electrode. In yet another approach step 708 can involve applying
the mixed suspension to the surface of the electrode, the electrode being
arranged in a magnetic field between approximately 0.05 Tesla and
approximately 2 Tesla and preferably the magnetic field is approximately
2 Tesla.

[0228]An alternative embodiment involving steps 702' through 714' (also
shown is FIG. 17) involves the use of an external magnetic field. That
is, again the method of making an electrode with a surface coated with a
composite with a plurality of boundary regions with magnetic gradients
having paths to the surface of the electrode when the external magnetic
field is turned on. The steps 702 through 714 are then modified into
steps 702' through 714' as follows. Step 702' involves mixing a first
solution which includes a suspension of at least 5 percent by weight of
inert polymer coated microbeads containing between 10 percent and 90
percent magnetizable non-permanent magnet material having diameters at
least 0.5 micrometers in a first solvent with a second solution of at
least 5 percent of ion exchange polymers in a second solvent to yield a
mixed suspension. Step 708' then involves applying the mixed suspension
to the surface of the electrode. Step 714' involves evaporating the first
solvent and the second solvent to yield the electrode with a surface
coated with the composite having a plurality of boundary regions with
magnetic gradients having paths to the surface of the electrode when the
external magnet is turned on.

[0229]FIGS. 18A and 18B show a flux switch 800 to regulate the flow of a
redox species according to yet another embodiment of the invention. In
particular, FIGS. 18A and 18B show an electrode 804 and a coating 808 on
the electrode 804. Coating 808 is formed from a composite which includes
magnetic microbead material 812 with an aligned surface magnetic field.,
an ion exchange polymer 816; and an electro-active polymer 820 in which a
first redox form is paramagnetic and a second redox form is diamagnetic,
wherein the flux switch is actuated by electrolyzing the electro-active
polymer from the first redox form ordered in the magnetic field
established by the coating to the second redox form disordered in the
magnetic field.

[0230]Microbead material 812 can include organo-Fe material. The redox
species can be more readily electrolyzed than the electro-active polymer.
Electro-active polymer 820 can be an electro-active liquid crystal with
chemical properties susceptible to said magnetic field or an
electro-active liquid crystal with viscosity susceptible to said magnetic
field. Electro-active polymer 820 include an electro-active liquid
crystal with phase susceptible to said magnetic field. Electro-active
polymer 812 can include poly(vinyl ferrocenium). In addition, the
externally applied magnetic field, and wherein said magnetic microbead
material comprises organo-Fed material.

[0231]FIG. 19 shows a dual sensor 900 for distinguishing between a first
species (particles A) and a second species (particles B). The dual sensor
includes a first membrane sensor 906 which preferentially passes the
first species over the second species; and a second membrane sensor 912,
which preferentially enhances the concentration of the second species
over the first species, thereby enabling the measurement of at least the
first species. The first and second species can be in any state such as
liquid, gaseous, solid and plasma.

[0232]In one embodiment, the first species can include a paramagnetic
species and the second species can include a diamagnetic species. In this
case, the first membrane sensor 906 is a magnetically modified membrane
sensor, and the second membrane sensor 912 is an unmodified membrane
sensor. The magnetically modified membrane sensor preferentially enhances
the concentration of and allows the detection of the paramagnetic species
over the diamagnetic species and the unmodified membrane sensor enhances
the concentration of and allows the detection of the diamagnetic species
and the paramagnetic species, enabling the measurement of the
concentration of at least the paramagnetic species. More particularly,
the paramagnetic species can be one of O2, NO2, and NO. The
diamagnetic species can be CO2.

[0233]In another embodiment, the first species can include a paramagnetic
species and the second species can include a nonmagnetic species. In this
case, the first membrane sensor 906 is a magnetically modified membrane
sensor, and the second membrane sensor includes an unmodified membrane
sensor. The magnetically modified membrane sensor preferentially enhances
the concentration of and allows the detection of the paramagnetic species
over the nonmagnetic species and the unmodified membrane sensor enhances
the concentration of and allows the detection of the nonmagnetic species
and the paramagnetic gaseous species, thereby enabling the measurement of
the concentration of at least the paramagnetic species. More
particularly, the paramagnetic species can be one of O2, NO2, and NO.

[0234]In yet another embodiment, the first species can include a
diamagnetic species and the second species can include a second
diamagnetic species. In this case, the first membrane sensor 906 is a
magnetically modified membrane sensor, and the second membrane sensor 912
is a differently magnetically modified membrane sensor. The magnetically
modified membrane sensor preferentially enhances the concentration of and
allows the detection of the first diamagnetic species over the second
diamagnetic species and the differently magnetically modified membrane
sensor enhances the concentration of and allows the detection of the
second paramagnetic species and the diamagnetic species, enabling the
measurement of the concentration of at least the first diamagnetic
species. The first diamagnetic species can include CO2.

[0235]In yet another embodiment, the first species can be a first
paramagnetic species and the second species can be a second paramagnetic
species. In this case, the first membrane 906 is a magnetically modified
membrane sensor, and the second membrane 912 is a differently
magnetically modified membrane sensor, wherein the magnetically modified
membrane sensor preferentially enhances the concentration of and allows
the detection of the first paramagnetic species over the second
paramagnetic species and the differently magnetically modified membrane
sensor enhances the concentration of and allows the detection of the
second paramagnetic species and the first paramagnetic species, enabling
the measurement of the concentration of at least the first paramagnetic
species. Again, the first paramagnetic species is one of O2,
NO2, and NO.

[0236]In yet another embodiment of the invention, the first species can be
a diamagnetic species and the second species can be a nonmagnetic
species. In this case, the first membrane sensor 906 is a magnetically
modified membrane sensor, and the second membrane sensor 912 is an
unmodified membrane sensor, wherein the magnetically modified membrane
sensor preferentially enhances the concentration of and allows the
detection of the diamagnetic species over the nonmagnetic species and the
unmodified membrane sensor enhances the concentration of and allows the
detection of the nonmagnetic species and the diamagnetic species,
enabling the measurement of the concentration of at least the diamagnetic
species.

[0237]FIG. 20 shows a cell 201 according to another embodiment of the
invention. In particular, FIG. 20 shows an electrolyte 205 including a
first type of particles. A first electrode 210 and a second electrode 215
are arranged in electrolyte 205. The first type of particles transform
into a second type of particles once said first type of particles reach
said second electrode 215. Second electrode 215 has a surface with a
coating 225 fabricated according to the above methods. Coating 225
includes a first material 230 having a first magnetism, a second material
234 having a second magnetism, thereby creating a plurality of boundaries
(33 of FIG. 15A) providing a path between said electrolyte 205 and said
surface of said second electrode 215. Each of said plurality of
boundaries having a magnetic gradient within said path, said path having
an average width of approximately one nanometer to approximately several
micrometers, wherein said first type of particles have a first magnetic
susceptibility and said second type of particles have a second magnetic
susceptibility and the first and said second magnetic susceptibilities
are different. Coating 225 operates in the manner described with respect
to FIG. 16.

[0238]First material 230 in coating 225 can include a paramagnetic species
and said second material 234 can include a diamagnetic species.
Alternatively, first material 230 can include a paramagnetic species
having a first magnetic susceptibility and the second material 234 can
include a paramagnetic species having a second magnetic susceptibility,
and said first magnetic susceptibly is different from said second
susceptibility. In yet another approach, said first material 230 can
include a diamagnetic species having a first magnetic susceptibility
while said second material 234 includes a diamagnetic species having a
second magnetic susceptibility, and said first magnetic susceptibly is
different from said second susceptibility. In another approach, the first
material 230 could alternatively include a paramagnetic species having a
first magnetic susceptibility and said second material 234 comprises a
nonmagnetic species. In another approach, said first material 230 can
include a diamagnetic species having a first magnetic susceptibility and
said second material 234 can include a nonmagnetic species. Electrolyte
can be an electrolyzable gas such as O2 or can include a
chlor-alkali.

[0239]While not wishing to be bound by theory, it is thought that the
reaction proceeds faster in the presence of a magnetic field, which
suggests higher rates for nickel metal hydride batteries charge and
discharge. The higher peak currents for magnetized electrodes also means
that battery resistance is reduced with magnetic field and could increase
batteries capacity and working potential.

[0240]Numerous and additional modifications and variations of the present
invention are possible in light of the above teachings. It is therefore
to be understood that within the scope of the appended claims, the
invention may be practiced otherwise than as specifically claimed.

[0241]The foregoing embodiments and advantages are merely exemplary and
are not to be construed as limiting the present invention. The present
teaching can be readily applied to other types of apparatuses. The
description of the present invention is intended to be illustrative, and
not to limit the scope of the claims. Many alternatives, modifications,
and variations will be apparent to those skilled in the art. In the
claims, means-plus-function clauses are intended to cover the structures
described herein as performing the recited function and not only
structural equivalents but also equivalent structures.

Electrosynthesis

[0242]It has been found that for the free radical systems, if charge and
spin are localized in the same atoms of a molecule, no magnetic field
effect is observed cyclic voltammetrically. However, if charge and spin
are dispersed or localized in different areas of a molecule, magnetic
field effects are observed. Thus, by employing magnetically modified
electrodes in electrosynthetic processes where radical intermediates do
not have charge and spin density localized on the same atom, it may be
possible to change reaction pathways and/or reaction rates.

[0243]The implications of such uses of magnetically modified electrodes
are far reaching, since they may be applied to any system having radical
intermediates. According to the present invention, one can determine
whether charge and spin density are localized on the same atom. If charge
and spin density are not localized, the use of magnetically modified
electrodes in the electrochemical process may enhance the rate of
reaction or change reaction pathways in the process.

[0244]Therefore, a preferred embodiment of the present invention is
directed to a method for enhancing an electrosynthetic process having
radical intermediates, which comprises determining the structure of
radical intermediates present in an electrosynthetic process; performing
spin and charge density calculations for the radical intermediates; and
employing a magnetically modified electrode in the process, provided that
charge and spin density are not localized on the same atom of said
radical intermediates.

[0245]Another preferred embodiment of the present invention is directed to
an improvement on conventional electrosynthetic processes. According to
such embodiments, in an electrosynthetic process having radical
intermediates, the improvement comprises performing spin and charge
density calculations for the radical intermediates; and employing a
magnetically modified electrode in the process, provided that charge and
spin density are not localized on the same atom of the radical
intermediates.

[0246]According to such embodiments, the magnetic particles may be either
coated or uncoated and may be employed as part of a coating layer on a
substrate material, such as Nafion or other conductive polymeric
materials having magnetic particles incorporated therein formed on a
substrate material.

[0247]Alternatively, an electrode made from a magnetic material may be
employed in the electrosynthetic process. Such magnetic materials
include, but are not limited to Ni, Fe, Co, NdFeB, Sm2O7,
combinations thereof and other magnetic materials known in the art.
According to certain preferred embodiments of the present invention, such
magnetic materials have a coating layer including magnetic particles
formed thereon.

[0248]The substrate material may be glass, metal, polymeric, a
semiconductor, conductive, such as graphite, magnetic or combinations
thereof.

Electrochromic Devices

[0249]Electrochromic cells comprise a thin film of an electrochromic
material, i.e. a material responsive to the application of an electric
field of a given polarity to change from a high-transmittance,
non-absorbing state to a lower-transmittance, absorbing or reflecting
state and remaining in the lower-transmittance state after the electric
field is discontinued, preferably until an electric field of reversed
polarity is applied to return the material to the high-transmittance
state. The electrochromic film is in ion-conductive contact, preferably
direct physical contact, with a layer of ion-conductive material. The
ion-conductive material may be solid, liquid or gel. The electrochromic
film and ion-conductive layers are disposed between two electrodes.

[0250]As a voltage is applied across the two electrodes, ions are
conducted through the ion-conducting layer. When the electrode adjacent
to the electrochromic film is the cathode, application of an electric
field causes darkening of the film. Reversing the polarity causes
reversal of the electrochromic properties, and the film reverts to its
high transmittance state. Typically, the electrochromic film, e.g.
tungsten oxide, is deposited on a glass substrate coated with an
electroconductive film such as tin oxide to form one electrode. The
counter electrodes include a carbon-paper structure backed by a similar
tin oxide coated glass substrate or a metal plate.

[0251]Examples of ion conductive materials used in electrochromic devices
is methyl viologen and other organic redox species. According to an
embodiment of the present invention, a magnetically modified electrode is
employed in an electrochromic device. Preferably, the electrochromic
device comprises an organic redox species having charge and spin density
not localized on the same atoms in at least one of the oxidized or
reduced forms. For instance, magnetic particles may be incorporated into
at least one of the electrodes or onto a surface of at least one of the
electrodes, such as a coating layer containing magnetic particles
dispersed in a medium, such as a polymer, metal oxide, or the like,
formed on an electrode surface. Examples of electrochromic devices are
disclosed in U.S. Pat. Nos. 5,215,821; 4,786,865; 4,726,664;
4,645,3074,773,741 and 4,818,352, each of which is incorporated herein in
its entirety.

Spectroelectrochemical Sensors

[0252]Another use of the present invention is in spectroelectrochemical
sensors. Such sensors are used, for instance, to measure the presence of
contaminants in a composition, e.g., metals such as the pertechnate ion
(TcO4.sup.-) and organic compounds such as methyl viologen, as well
as to measure the relative amounts of compounds in a mixture, such as CO
and O2.

[0253]A typical spectroelectrochemical sensor includes an optically
transparent electrode coated with a selective film. Sensing is based on
the change in the optical signal of light passing through the OTE that
accompanies an electrochemical reaction of an analyte at the electrode
surface. Examples include a glass substrate coated with indium tin oxide
or another conductive, optically transparent material. Such sensors also
may include with a selective polymeric coating, such as a cation
selective Nafion-SiO2 film or an anion selective PDMDAAC-SiO2
film, where PDMDAAC=polydimethyldiallylammonium chloride.

[0254]It has been found according to the present invention, that such
sensors may be enhanced by incorporating magnetic particles at or near
the electrode surface. For instance, magnetic particles may be added to
the selective metal oxide coating. Alternatively, magnetic particles may
be dispersed in the selective polymeric coating.

Experimental

[0255]Cyclic voltammetry was performed on each organic redox couple at
both a Nafion modified electrode and a magnetic microsphere/Nafion
composite modified electrode. Ab initio calculations of spin and charge
density were performed on each organic redox couple in. its free radical
oxidation state.

[0256]I. Reagents

[0257]The following redox couples were examined:
N,N,N',N'-tetramethyl-1,4-phenylenediamine, anthracene,
9,10-dimethylanthracene, 9,10-diphenylanthracene,
tetracyanoquinodirnethane, thianthrene,
2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphine nickel(II),
1,4-benzoquinone, benzyl viologen dichloride, rubrene, and methyl
viologen dichloride. All were used as received from Aldrich. Solutions
and were made in HPLC Grade acetonitrile (Fisher) that was dried over
molecular sieves. The concentration of the redox species was 1 mM with
0.1 M tetrabutylammonium tetrafluoroborate (SACEM) electrolyte.

[0258]II. Electrode Preparation

[0259]A glassy carbon disk working electrode (A=0.459 cm2) was
polished with 1.0 μm, 0.3 μm, and 0.05 μm alumina, successively,
on Svelt polishing clothes (Buehler). The electrode was then sonicated
for 5 minutes in 18 MΩ water to remove remaining alumina. The
electrode was soaked in concentrated nitric acid for 2 minutes and
thoroughly rinsed with 18 MO water.

[0260]The electrode surface was modified with either a Nafion film or a
magnetic micro sphere/Nafion composite. Nafion films were prepared by
pipetting an appropriate volume of 5% by wt. Nafion solution onto the
electrode surface. The magnetic microparticle/Nafion composite were
prepared by pipetting an appropriate volume of composite stock solution
on the electrode surface in the presence of an external cylindrical
magnet (6.4 cm O.D., 4.8 cm I.D., 3.2 cm, 8 lb. pull, approximately 0.25
Telsa, McMaster-Carr).

[0261]The composite stock solution was prepared by adding fractions of 5%
by wt. Nafion solution and 2.5% by wt. Polysciences paramagnetic
microsphere solution (polystyrene shrouded iron oxide spheres, 1-2 μm
in diameter). The fractions were calculated so that the dry composite
film was composed of 10% by weight magnetic microspheres and 90% by
weight Nafion. All films thickness were 5.1 μm. After the modified
electrodes were dried in the external magnet, they were placed in a
vacuum desiccator overnight to ensure thorough removal of casting
solvents.

[0262]III. Electro Chemical Measurements

[0263]Electrochemical flux of each redox species through the membrane
layer to the electrode surface was studied using cyclic voltammetry.
Nafion film and magnetic microparticle/Nafion composite modified working
electrodes were equilibrated in 1 mM redox couple and 0.1 M
tetrabutylammoniumtetrafluoroborate for 30 minutes before measurements
were taken. To eliminate interferences from overlapping peaks and
quenching by oxygen, the solutions were degassed with nitrogen during
both equilibration and experiment.

[0264]The reference electrode was a silver wire. The counter electrode was
an approximately 1 in2 piece of platinum gauze spot welded to
platinum wire. Data were collected and analyzed on a Pentium computer
interfaced to a BioAnalytical Systems Model 100B/W Potentiostat. Cyclic
voltammetry was performed at scan rates ranging from 50 to 200 mV/s.

[0265]For cyclic voltammetry, peak currents (ip) and peak potentials
were the diagnostics of kinetic changes. Peak currents (ip) provided
information about the apparent diffusion coefficient of the redox species
and other kinetic information. The mass transfer limited peak current
expression is provided in Equation 5.

ip(v)=(2.69×105)n3/2ADapp1/2v1/2.di-el-
ect cons.kC* (5)

where n is the number of electrons transferred, F is Faraday's constant, A
is the area of the electrode, v is the scan rate, .di-elect cons. is the
porosity of the film, and C* is the concentration of the redox species in
solution. The extractions and apparent diffusion coefficients are k and
Dapp.r respectively.

[0266]IV. Spin and Charge Density Calculations

[0267]Ab initio spin and charge density calculations were done for all
free radical intermediates. The geometry was optimized and density
calculations were performed using Gaussian 94W for a variety of different
basis sets. The data presented in the following Tables are for the
largest basis set. Further increases in the size of the basis set did not
alter the calculated results.

[0268]V. Redox Couples

[0269]A. Methyl Viologen

[0270]Methyl viologen dication is an organic molecule that is commonly
used in spectroelectrochemistry. The chemical structure of methyl
viologen dication is shown in FIG. 21. Methyl viologen dication undergoes
two single electron transfers. The first single electron transfer forms a
methyl viologen cation radical. The second single electron transfer
reacts with the cation radical to form neutral methyl viologen.

[0271]A typical cyclic voltammogram of methyl viologen at a Nafion
modified electrode and at a 10% by wt. magnetic microsphere/Nafion
composite modified electrode are shown in FIG. 22. The cyclic
voltammogram shows an increase in the peak currents for all electron
transfer processes at the magnetically modified electrode. These flux
enhancements are more about 40%.

[0272]The spin and charge density calculation results for methyl viologen
are presented in the FIG. 23. The sum of charge density is +1.0 and the
total sum of spin density is 1.0. The spin is localized on C1, C3, N1,
and N2. C1 and C3 are the two methyl carbons attached to the nitrogens.
Therefore, all of the spin density is concentrated on the methyl ends of
the molecule. Some negative charge density is localized on the two
nitrogens, but the positive charge density is dispersed through all the
hydrogens in the molecule. C1 and C3 have very little charge density.

[0273]B. Benzyl Viologen

[0274]The chemical structure of benzyl viologen dication is shown in FIG.
24. Benzyl viologen has similar electrochemistry to methyl viologen, as
shown in FIG. 25 for the cyclic voltammetry of benzyl viologen at Nafion
and magnetic composite modified electrodes.

[0275]For benzyl viologen, peak currents for both anodic and cathodic
peaks of both electron transfers are enhanced. The enhancements range
from 75%-300% depending on the stability of the film. This is a dramatic
magnetic effect on the electron transfer kinetics of an organic molecule.
There are also substantial shifts in peak potentials. The difference
between the cathodic and anodic peak potentials increases by
approximately 200 mV in the presence of the magnetic field.

[0276]The spin and charge density calculation results for benzyl viologen
radical are shown in the FIG. 26. The spin and charge density
calculations are similar to those for methyl viologen. The total charge
is 1.0 and the total spin is 1.0. There is very little spin or charge
density localized in the 2 benzyl groups. The spin density is centered on
the C1, C3, N1, and N2 atoms. The carbons C1 and C3 are the benzyl
carbons attached to the nitrogens. The negative charge density is
centered on the nitrogen atoms, but the positive charge density is
delocalized throughout the structure.

[0277]C. Benzoquinone

[0278]Benzoquinone is an organic molecule that is commonly studied
electrochemically. The structure of benzoquinone is shown in FIG. 27.
Benzoquinone can undergo two single electron transfers. The first single
electron transfer forms a semiquinone radical. The second single electron
transfer reacts to semiquinone radical forms a diamagnetic benzoquinone
di-anion.

[0279]A typical cyclic voltammogram of benzoquinone at a Nafion modified
electrode and at a 10% by wt. magnetic microsphere/Nafion composite
modified electrode is shown in FIG. 28. There is no significant
difference between the cyclic voltammetry of the Nafion film coated
electrode and the 10% by wt. magnetic microsphere/Nafion composite
modified electrode. Therefore, there are no appreciable magnetic field
effects on the heterogeneous and homogeneous electron transfer reactions
occurring in this system. It should be noted that in aqueous matrices,
the behavior of hydroquinone is significantly impacted by magnetic
modification.

[0280]FIG. 29 shows the spin densities and charge densities of the
semiquinone radical that were calculated using ab initio calculations.
The total charge is -1.0 and the total spin is 1.0. The spin and charge
density are both centered mainly on the oxygen atoms, O1 and O2.

[0281]D. Diphenylanthracene

[0282]Diphenylanthracene is an organic redox couple that is commonly used
in electrochemiluminescence studies. The chemical structure of
diphenylanthracene is shown in FIG. 30. Diphenylanthracene can be
oxidized and reduced to form either a cation radical or an anion radical.

[0283]A typical cyclic voltammogram of diphenylanthracene in a Nafion film
and a 10% by wt. magnetic microsphere/Nafion composite can be seen in
FIG. 31. The larger cyclic voltammogram without the reverse oxidation
wave is for the magnetic composite.

[0284]The cyclic voltammetric peaks at approximately -1.75 V correspond to
reduction of diphenylanthracene to diphenylanthracene anion radical and
oxidation of diphenylanthracene anion radical to diphenylanthracene. Peak
currents increase 2-3 fold for the magnetic microsphere/Nafion composite,
and there is no reverse peak for the magnetic microsphere/Nafion
composite. While not wishing to be bound by theory, this suggests that
there is a probability the diphenylanthracene anion radical is either
being stabilized in the presence of the magnetic field or undergoing a
homogeneous reaction path. The cyclic voltammetric peaks at approximately
1.3-1.5 V correspond to oxidation of diphenylanthracene to
diphenylanthracene cation radical and reduction of diphenylanthracene
cation radical to diphenylanthracene. There are small peak current
increases for the magnetic microsphere/Nafion composite during the
oxidation process, but a decrease in relative peak currents for the
reduction back to diphenylanthracene.

[0285]The spin and charge density calculation results for
diphenylanthracene anion radical are shown in the FIG. 32. The total spin
is 1.0 and the total charge is -1.0. The spin density is centered at C7
and C8 which are the center carbons on the middle ring at the 9,10
positions. The charge density is delocalized throughout the molecule.

[0286]The spin and charge density calculation results for
diphenylanthracene cation radical are shown in the FIG. 33. The total
spin is 1.0 and the total charge is 1.0. The spin density is localized on
C7 and C8, but the charge density is delocalized throughout the molecule.

[0287]E. Dimethylanthracene

[0288]Dimethylanthracene is an anthracene analog that is similar in
structure and chemistry to diphenylanthracene. The chemical structure of
dimethylanthracene is shown in FIG. 34. The cyclic voltammetry of
dimethylanthracene reduction to dimethylanthracene anion radical is shown
in FIG. 35. The cyclic voltammetry of dimethylanthracene oxidation to
dimethylanthracene cation radical can be seen in FIG. 36.
Dimethylanthracene shows the same trend in magnetic effects that
diphenylanthracene does. A large flux enhancement for the formation of
the anion radical, but a much smaller (or negligible) magnetic effect for
the formation of dimethylanthracene cation radical.

[0289]The spin and charge density calculations for dimethylanthracene
anion radical are presented in FIG. 37. The spin and charge density
calculations for dimethylanthracene cation radical are presented in FIG.
38. The sum of the spin densities for both radicals is 1.0. The total
charge of the anion radical is -1.0 and the total charge of the cation
radical is 1.0. The charge density is delocalized throughout the
molecule, but the spin density if concentrated on C7 and C8, which are
the center carbons on the middle ring.

[0290]F. Anthracene

[0291]Anthracene is a common organic redox couple. The chemical structure
of anthracene can is shown in FIG. 39. Anthracene undergoes
electrochemistry similar to that of diphenylanthracene and
dimethylanthracene. The cyclic voltammetry of anthracene is shown in FIG.
40.

[0292]The spin and charge density calculations for anthracene anion
radical are presented in FIG. 41. The spin and charge density calculation
for anthracene cation radical are presented in FIG. 42. The sum of the
spin densities of both radicals is 1.0. The total charge of the anion
radical is -1.0. The total charge of the cation radical is 1.0. The
charge density of both radicals is delocalized over the whole molecule.
The spin density of both of the radicals is concentrated on C7 and C8,
which are the center carbons on the middle ring.

[0293]G. Rubrene

[0294]Rubrene is a large organic redox couple. The chemical structure of
rubrene is shown in FIG. 43. The electrochemistry of rubrene is similar
to other anthracene analogs, except that the peaks are shifted slightly.
Therefore, only one electron transfer step is within the potential window
for acetonitrile. The electrochemistry of rubrene in acetonitrile is
shown in the cyclic voltammograms in FIG. 44. Rubrene is reduced to
rubrene anion radical. The current is somewhat enhanced for the magnetic
composite.

[0295]The spin and charge density calculation results are shown in the
FIG. 45. The total spin is 1.0 and the total charge is -1.0. The spin is
localized on C7, C8, C23, and C24, which are the middle carbons on the
center rings to which the phenyl groups are attached. The charge density
is delocalized throughout the molecule.

[0296]H. Tetracyanoquinodimethane

[0297]Tetracyanoquinodimethane is an organic redox couple that undergoes
two single electron transfers. The chemical structure of
tetracyanoquinodimethane is shown in FIG. 46. Tetracyanoquinodimethane
can be reduced to its anion radical. Then, it can be further reduced to
the diamagnetic di-anion. The cyclic voltammetry of
tetracyanoquinodimethane at a Nafion modified electrode and a magnetic
microsphere/Nafion modified electrode are shown in FIG. 47.

[0298]Tetracyanoquinodimethane shows negligible magnetic field effects in
the cyclic voltammogram. Therefore, there are no appreciable changes in
heterogeneous and homogeneous electron transfer kinetics. The spin and
charge density calculations are shown in FIG. 48. The total spin is 1.0
and the total charge is -1.0. The spin density is localized at the 2
nitrogen atoms attached to the same carbon. The negative charge density
is also localized at the nitrogen atoms.

[0299]I. Tetramethylphenylenediamine

[0300]Tetramethylphenylenediamine (FIG. 49) is commonly known as Wurster's
Reagent. It is used frequently in spectroelectrochemistry.
Tetramethylphenylenediamine undergoes two single electron transfer steps.
The first electron transfer occurs when tetramethylphenylenediamine
oxidizes to tetramethylphenylenediamine cation radical. The second
electron transfer occurs when tetramethylphenylenediamine cation radical
is oxidized to diamagnetic teftamethylphenylenediamine dication.

[0301]The electrochemistry at Nafion and magnetic microsphere/Nafion
composite modified electrodes can be seen from the representative cyclic
voltammograms in FIG. 50. In this system, the larger cyclic voltammogram
is the Nafion film and the smaller cyclic voltammogram is the 10% by wt.
magnetic microsphere/Nafion composite modified electrode. The cyclic
voltammetry shows decreases in electrochemical flux and morphological
changes, including an asymmetric increase in the prewave of the second
electron transfer step.

[0302]The results of the spin and charge density calculation are shown in
the FIG. 51. The spin density is localized on the nitrogen opposite from
that where the negative charge density is localized.

[0303]J. Thianthrene

[0304]Thianthrene is an organic molecule similar to anthracene except that
two carbon atoms are replaced with sulfur. The chemical structure of
thianthrene is shown in FIG. 52. Thianthrene is oxidized to form a
radical cation. The radical cation is further oxidized to form a
dication.

[0305]Cyclic voltammetry of thianthrene at Nafion and magnetically
modified electrodes is shown in FIG. 53. Given a stable film, there is
little or no magnetic field effect on the cyclic voltammetry. In some
cyclic voltammograms, small morphological changes appear, but they are
characteristic of unstable films.

[0306]The spin and charge density for thianthrene radical calculation are
given in FIG. 54. The total spin and total charge are 1.0. The positive
charge density is localized at the sulfur atoms. The spin density is also
localized at the sulfur atoms.

[0307]K. Octaethylporphine Nickel(II)

[0308]The octaethylporphine nickel(II) free radical redox couple was
studied in methylene chloride solvent This nickel porphrine is uncharged.
The chemical structure of octaethylporpbine nickel(II) is shown in FIG.
55. In the methylene chloride potential window, octaethylporphine is
oxidized to the octaethylporphine nickel cation and then subsequently
oxidized again to the dication. It is important to note that the ring is
undergoing oxidation and not the nickel center. The cyclic voltammetry of
octaethylporphine nickel(II) at Nafion and magnetically modified
electrodes is shown in FIG. 56. Gaussian has been unable to perform
geometry optimization of octaethylporphine nickel(II) for all basis sets.
Therefore, there is no spin and charge density information for this
molecule.

[0309]L. Discussion

[0310]Magnetic field effects on free radical electrochemistry in
acetonitrile solution are smaller than the analogous magnetic field
effects on transition metal complex electrochemistry in water. For the
free radical systems, if charge and spin are localized in the same atoms
of a molecule, no magnetic field effect was observed cyclic
voltammetrically. However, if charge and spin are dispersed or localized
in different areas of a molecule, magnetic field effects are observed.

[0311]The above results are summarized into FIG. 57. It is noted that the
largest effects are observed for benzyl viologen and the anthracene-based
anion radicals. The magnitude of the magnetic effect (flux enhancement)
is determined to be no effect if less than 10% on average, small effect
if between 10 and 40% on average, medium effect if between 40 and 80% on
average, large if greater than 80% enhancement on average, and
morphological if the cyclic voltammograms showed altered shape.

[0312]This comparison of spin and charge densities does not provide a
quantitative assessment of flux enhancements or morphological changes.
However, it is effective at determining whether a magnetic effect will be
observed. Further, it is noted that magnetic effects are diminished by
heteroatoms as they are more electronegative and localize charge and spin
density.